It's kinda hard for me to put my thoughts into words, and this situation isn't helping, so bear with me.

I've been with my girlfriend for four years. We had our problems through the years but we've worked through them and I'm generally happy with her. We've been living together for a good three years now and a few months ago I proposed. Everything was fine for a little while after that but lately...I don't know whats going on. More and more these little things she does start annoying me. Things she did that I used to think were cute or quirky are now starting to look stupid to me. Her jealousy, which was mildly tollerable, is now almost on the verge of insanity.

Normally, I'd just keep dealing with this my way (keep it all inside because that's the type of person I am and I've been though similar situations before) but there's a twist this time.

We have a friend who we've known for as long as we've been together. I'm not going to lie, from the moment I met her I've found her extremely attractive. I pushed those feeling aside because we were both in relationships. However, the more we all hung out the more I started seeing that she and I are more in tune with each other. Recently, me and her had a chance to hang out alone (something that never happens because of my girlfriends jealousy) and we got very close. In addition to realizing that we had a lot more in common than I thought all the old suppressed feelings came back out. Some stuff happened that night (no sex, no kissing) and while it did weird us both out, we both agreed that it felt really good.

I have no clue what I'm supposed to do or think. Four years is a long time for me (longest relationship I've had is this one) and there's a lot invested; but I don't know if I'm making the right decision by staying with my fiance. Our friend is having issues with her relationship right now but I doubt anything would happen between us if I just up and ran to her...I think.

I really need some help here...