facing the facts

ok, so here it is. I've never claimed to be a perfect human being, but who is? I do my best though. I go to school, work, pay my bills, etc. But when it comes to matters of the heart I tend to...well, do what I want....
Basically, I started a man that used to date a friend. His version is very different than hers, and based on her side of things and past conversations, I do believe his. I remember telling her on numerous occasions, 'honey, it's time to let it go. He's no into you'. But she never listened and according to him, she pretty much stalked him for about 3-4 months after he told her it was over. Anyways, details are WAY too much to get into.
Moving forward... We ran into each other at a bar that we all love to go to. She was out of town or something, he was there alone. I saw him and we started talking up a storm. I'd just broke up with, yet another boyfriend. (yeah, I've dated a few guys since Jason and I broke up). And he went OFF about him and 'sukra' and how that all went down, blah blah blah.
Yeah... we left together. And Yes, we slept together. And Yes, I thought it was just going to be a one night stand (my first one!!!). Since we were kind of friends before that happened, we ended up chatting here and there and just stayed in touch, but nothing romantic at all. I had another new boyfriend and he was dating a girl quite seriously too. So it was completely harmless.
As fate would have it, after he came back from Boston we started going to the gym together almost everyday and one night we had drinks. I'm sure you can imagine what took place next. But here's the thing, it's more than that now. It's been going on now for about 3 weeks. We hit the gym all the time, which is totally cool!, and we hang out several times throughout the week. We've established that we are sleeping together monogamously, and that we really like each other.
So, with that said... it bring me to the 'truth'. It's time to tell her. Everyone else knows, meaning mutual friends. We haven't exactly tried to keep in on the DL for the past lil while and I'm sure she's seen my car parked in front of his house more than once in the last lil while. Not to mention the pics he posted of us on my facebook and his....
AHHH!! I am not a terrible person. It just happened. But what do I say? She thinks she was in love with him. And he HATES her!!! and I really like him and he really likes me!!!
SHIT!