An awkward situation

Hi guys, hoping to get some advice here.

For quite some time now I have been in love with a close friend of mine. We got speaking again after a few years of not seeing each other about 6 months ago or so. I was attracted to her some years back when we first met but never made a move because of the circumstances at the time.

We spend a lot of time together, text each other a lot, randomly pop in to see each other at work and I feel such a connection to her that I can tell her anything...except what I really want to tell her. Those three words.

The complications start in that she is engaged, I am not the type of person to break up a relationship or disrespect their relationship. I know for a fact she has had feelings for me of some sort in the past but am unsure as to what they are these days. She did say to me recently that it's a shame we didn't get talking again sooner, meaning that there could have been something between us should we have met again before she met her current partner.

She's an extremely friendly, laid back girl that has a lot of male friends, but I am easily the only one she spends time alone with and a lot of time with. I know I have no right to but I get jealous when she does see other Male friends because of the way I feel about her.

I only ever seem to be my happiest when i'm around her these days or when we're talking via text etc. I feel we have a real connection and could be so happy together. But at the same time I feel like i'm just kidding myself to think she'd ever wanna be with a guy like me (yes I have some self esteem issues)

I don't quite know what advice i'm expecting here, I do not want to lose her friendship but I do wish I could let her know how I feel without it seeming like I have an agenda to break her away from her fiancee.

Any advice at all with regards to anything would be greatly appreciated. Thanks