How do I keep feelings from ruining my friendship?

It sucks just admitting it, but I'm falling big time for an older, married co-worker. That doesn't describe it - I'm actually obsessing like a desperate teenager about her... my poor sick mind can't do else but absorb any information related to her that comes across...
Where it started: last year, after finishing my studies I applied for a full-time job that really interested me, in a completely new city. I was free of commitments (just out of a 2-year relationship) and still young - 24 now - so I thought I'd just enjoy the new experience. So last year in October, after training, I was moved to the office where I'd work from there on, one populated with men and women of all ages.

That's where I met V and she stood out from the rest of the women in only 1 way: besides the boss (also a woman) she was the only one who had a friendly and welcoming attitude to me - the other girls in the office were either going into flirty mode or pretty much ignoring mes.
She tried to make me feel more comfortable in the group, she had been in the place for close to 4 years, so she knewl the spin of things. I was a bit reluctant to being befriended by a woman from the very first days in that office, for fear of the kind of unspoken labelling that it would get me from guys at the office (I was somewhat prejudiced about women back then).
Surprisingly enough, it went nothing like that. She was to say a bit 'bubbly' only my first day there, but after that she knew very well when, what or how much to speak to me as well. She discreetly came to help me out with workstuff when I couldn't find my way around and was too proud to ask and overall was never intrusive or trying too hard to be friendly.

She is 33 years old, married and mother of a 5 year-old. Based on looks only, she is not my type (or what I usually consider my type), but nevertheless petite and very feminine and... therefore attractive in her own, personal way...
So far anyone would say, it's no big deal that I would see her as different (in a good way) from the rest of women or even somewhat attractive, but that was all it was only for the first couple of weeks. After that, our relationship easily became one of great friendship. I was constantly amazed at how intuitive to my moods she was and how easy it was to talk and just be around her. I hadn't previously seen myself as adapt at reading and handling women's moods, but I needn't have any worry of that sort around her.
I have never before felt such an affinity to someone, but I just laid it all on her being a very empathic, understanding and non-judgmental person.

During work but mostly on lunch breaks we had the chance to talk about all sorts of things and I found out that although she's almost 10 years older than me, her tastes in music, books, movies and art are not much different than mine. They're not the same, of course, but she is always keeping an open mind, she's eager and quick to learn new things, really seems to listen and understand what I'm talking about (even if it's silly, unimportant things sometimes) and never made me feel like she knows much more than me just because she's some years older than me.

Her favorite subject is definitely her daughter and I'm being understanding as it's obvious that she loves her more than life, but it's really easy to talk to her and she will talk about just any subject. However there are a few (and starting to become bugging) exceptions: sex and generally intimate stuff and married-life related things. It seemed a bit strange to me and then kind of sad that she does her best to avoid being involved in discussions on these subjects when co-workers start them up. In some instances, some of the younger ones turned to her for advice (considering her age advantage) and she seemed totally cornered, just throwing some evasive answer to get out of it, those being the only times when she felt awkward and made the rest of us feel it too.

It's not that she cannot take a cheeky joke or allusion once in a while and she'll return it with skill, but it's a very different story when asking hert or getting her into a whole discussion about that...

I got the chance to meet her husband, once at the company's Christmas party (that was the only time I've seen her with him at an outing with people from work). I'll say that after observing him I couldn't make myself feel much shame about the unlawful nature of my feelings toward his wife. Yeah, maybe it would've been better if I didn't meet him and still imagined that he is a loving, caring husband, better than me in countless ways. But the truth obvious to any observer was that he is completely her opposite: majorly lacking social skills and didn't even try or care to seem nicer to his wife's colleagues.
I felt sad for her, now starting to understand why she very seldom mentions her husband when talking to anyone at the office and definitely never gives more personal details of their relationship (like some of the other girls at the office can't help but doing). I noticed she almost never talks to him on the phone at work, but I thought that was because he is extremely busy with his work and is frequently out of town on business.

As much as I wanted to talk to her about this, she never touched the subject and I couldn't just go ahead and ask her without causing her to become suspicious of my motives. I thought it best to wait till we got to know each other better and she would learn to trust me enough to confide in me about more personal issues. In the end, our friendship was going strong, I valued that above everything else (I still do) and didn't want to lose it by saying or doing something thoughtless.

That proved to be easy only in theory, as I found myself becoming more & more attracted to her and having her within sight 8 hrs/day (her desk is some 17 ft in front of mine) certainly didn't help. I could only get pissed at myself in too many occasions for finding myself sneaking looks at her body and observing her movements and gestures. It got worse when I found myself noticing some of her mannerisms at other women and thinking again about her, so bad I swear I wished to slap my own face in public at times to just get over this.

I remember slipping her a few subtle compliments about her looks or just encouraging her to be more confident about herself when she seemed to have some issues with self-confidence, but only in the early stages of our friendship, as later I couldn't do that anymore for fear that something else would also come through in my voice or show on my face.

She however seemed to take notice and in the last few months she made some changes, like wearing more youthful clothes and changing her haircut which got her plentiful praise from her colleagues. It still left me wondering if it had something to do with me because why would she do this only now, when the girls at work had been badgering her for long time before about freshening up her style.

Of course, I couldn't help trying to see if she feels any attraction towards me and it was funny/weird that I would try to act normal around her, all the while sizing up her reaction to my presence. I mean I'd never been that shy dude that cannot act on his interest for a girl, but in this case I didn't really have a choice... And I DID see signs that it made her nervous to be close to me, like avoiding to touch me, jumping a bit when that happened accidentally or quite noticeably blushing when being pressed to me in a very crowded elevator on the way to our floor.

At this point, it would seem like I was frustrated about not getting laid enough or something (for reading into so many stupid little details) but it wasn't the case. I met a girl in January and we've been seeing each other every week (usually in the weekends) and almost everytime we end up having sex. I think it's actually all that this is about, the most fun that we can have together is in the sack, because she didn't seem to be interested in going out with me or meeting each other's friends or even talking to me much.

However, things have taken sort of a turn for the worse last month, while on teambuilding weekend with all the people at work, at a mountain resort. It was a memorable weekend, she was even more fun to be around than at the office.
On the last night there, we had a dance party at the hotel's club and I naturally took the chance to dance with her. It was a slow dance and it proved even more difficult to keep my composure than I thought, once I was holding her so close, feeling her body warmth and perfume, it was like all my braincells self-distructed and I just couldn't form coherent sentences throughout the dance. I swear I haven't felt that awkward since I was like 16 and it seemed to affect her too: she tried making some little joke at the beginning, but then just got all quiet and just smiled uneasily and blushed when our eyes met.
Later in the evening, the air became unbreathable in the club, so she asked me if I wanted to step out to get away from the smoke and loud music. I followed her, we went for a walk and sat on a bench and talked for an hour or so. She was tired and a little tipsy so she was just speaking whatever crossed her mind. She was nothing short of adorable and I was impressed that even like this she had a dose of innocence that I've rarely seen even in girls of my age.
I was also surprised that when the conversation came around to the relationships topic, she didn't shut it down as usual. Her speech became quite emotionally charged and she said something on the lines of 'it is not fair to take advantage of the exclusivity that your partner has commited themselves to in their relationship to you and just take them for granted', as in not making anymore effort to keep the feelings alive and 'nobody deserves to feel an emotional prisoner just because they decided to entrust themselves to someone'. She didn't mention anything that would specifically relate to her situation, but I could it read it on her face that it was not just generally speaking, it was something that was affecting her personally.

It was really cold outside and she didn't have her jacket with her so I put mine on her shoulders, then she turned and looked me in the eyes and our faces were like 2 inches apart. I didn't move or even breathe but waited to see if I could move in for the kiss. But she didn't wait longer than 2 seconds until she sprung to her feet and let me know that she'll be going to her room to sleep, then added "enjoy the rest of the evening and see you tomorrow" and rushed to the elevator. Still wearing my jacket...

I thought this would make things much more awkward between the two of us, but it partly didn't - she didn't change her attitude towards me in presence of other people - and partly did, because since then she has a more 'guarded' posture in my presence (like arms crossed on her chest, keeping her chair at further distance from mine when looking at the same monitor), she doesn't sustain eye contact with me for longer than a few seconds even when we have to discuss workstuff and it's really not like her, it bothers me and I can see she's uneasy about it too. Same for her smile, it used to be sincere and heartwarming, now it's restrained and awkward.

I'm afraid that I will lose her friendship and lose her altogether and it's mostly my fault. I cannot help but feel miserable because I didn't ask to fall for her like this, hell, I wasn't looking to feel for any woman with the intensity that I feel for her.
I've already stooped so low once (I scared myself thinking about it afterwards) to kind of be a stalker: I went to the park one Sunday afternoon, because I remembered her mentioning that she would be taking her daughter there to play if the weather was fine. All that just because I couldn't wait until the next day to see her at the office... and I met her in the park... and her daughter... and seing how great they are together and how they love each other, it made my heart just melt and it made it even worse... and I would go home thinking how stupid I was to try seeing her outside work and that I should never do that again.

And unfortunately changing workplaces is just out of the question for both of us, I've moved to this city specifically for this job and we both got the best jobs available here and especially in these times...

I'm getting so pathetic I feel like smacking myself every time I think of it and I just couldn't make myself talk about it with no one else about her and this situation because I know beforehand what kind of replies I would get: either to go for it, it's many a man's dream to get with an older woman, just imagine how much I'd have to learn... or... to get my mind out of my pants, remember that not only she's married but she has a kid and I could be the cause of incommensurable damage, so just get over it as soon as I can. While I would agree with the latter, it doesn't present me any actual solutions for how to get it out of my system, but the people I know who would serve me this version would surely offer me a generous helping of criticism, cynism and then some pity...

I'm already aware that I cannot be the one to step up and mess her marriage, it just goes against how I was raised by my family in high consideration of family values. My parents are still together after 25 years and clearly care deeply about each other and hopefully I'll have that in my life too someday.

I couldn't talk to any of my friends about this, any of them would've fallen asleep or slam the door in my face half way through it. Bottom line conclusion is: I know I should probably act mature about it and not wait like a thief in the dark for her moment of weakness when she'd throw herself at me (although I must admit I've dreamt about this many times) and just not wait for anything but come forth and talk to her about what's happening to our friendship. Possibly come up with a big apology to make her understand that I'm not the dickhead she might think me to be sometimes.

And though I'm well aware that I should man up and do this, I have little to no clue about how I should I put this across in words. It's that difficult because we haven't really had serious talks outside work-related stuff (except maybe that one), we just like to keep it light, so I just can't think of how I should start this talk... I mean I don't want to sound too serious about it and completely scare her off, but not turn into a shallow-ass blab either....

So any suggestions would be welcome and thanks for sticking with me so far if you have!