What is wrong with me? Can i make a life with her?

[GhostsCantSee]

Hi,registered to these forums to try get some helpful advice on my love situation.

Ok, so i am 23, i am currently seeing my girlfriend/ex, and have been since last year june.

So, we have known eachother for around 5 years now, through working together orginally, we quite liked eachother 3/4 years ago, but working together kind of stopped us dating properly or ever becoming serious, however, 2 years ago we went own ways and changed careers an what not, and no longer work together.

We started talking/texting/social networking, in around may/june last year, instantly hit it off and went out for dinner, lunch, cinema etc over the period of 4/5 months, it was last year august we begun to date. It was going very very well, i loved (and still love!) her very much, as she loved me very much.

Things got messy this year however, my friend attended a party/get together, back in early june, and didn't drink that night due to driving, we had a big arguement the night before, she left with me not saying a word and she was pretty upset, but ultimately ended up kissing another man for a period of around 10/15 seconds, pulled away, kept quiet and told just one of her friends how bad and wrong she felt, she however decided to not spill out to me. It stayed quiet and under wraps for a week, she never spoke to the guy since and says she just wanted to forget it ever happened and never let anyone know, but however, i found out, i saw a text from her friend which definietely gave me an idea, and i questioned it several times, time and time again, until she finally quitted the "nothing happened" act, and spilled out to me what happened, how bad she felt, and that she'll do anything in the world for me to prove it was nothing and that it's me she loved.

I instantly, ended what he had, said i can'tbeat with someone who can do such an act, i don't understand how you can kiss someone whilst being in love with someone else,
so first question is, if you truely love someone, is it possible to make a mistake and let a man kiss you with no immediate reaction to stop what's going on? can it reallybe a mistake you'd never make again?
We didn't speak for a couple weeks, but truth is, i missed her loads, all mutuals had been telling me how cut up she is, had a week off work, and can't believe whats hapened, so i contacted her, we met up, got on, etc.

This was back in June, since then, we've been 'seeing eachother' without ever making our relationship official, we have had times when we get on well, and we've been seeing eachother practically daily.
She took me on a weekend away and paid for everything, probably in guilt, but said it was to make it up to me, and understand it wont make up for what she did but just try save what we had.

So yeah, i can tell she genuinly in sorry.

Anyway, my main concern, i know of the guy who did what he did. And my anger and biterness is still as strong as it was the second i found out, 5 months ago now it happened, and when i think and picture what happened, i get so wound up and angry, and it's the catalyst of 95% of the arguements we have now.
I love her so so so much though, you may call23 young, and that i can leave it and move on, but the feelings i have are very different and strong to this girl, and a big part of me says don't chuck what we have away for a silly kiss that means nothing, but then i think about things and say why am i giving a second of my time to a girl who hurt me so bad?

When will this anger and biterness go?! I'm not sure i trust her at the moment, i don't really know, again, big part of me says she'd never in a million years go near anyone again, but then i think if she can make 1 stupid decision, why can't she make another?
What i really want to know to, is, can someone really make this mistake when they are with someone they really love?

Thanks.

[Peter_rocks]

Time will ease things up surely. But, even though you think saying "23 is young" is lame but I can tell you it isn't. 23 is definitely young and the question is: you obviously can only have a very, very serious relationship with her: do you want that?
Are you sincerely sure she wouldn't do this again and are you sure her feelings are as strong?
This should be your main concern.