F***ed Up Situation

I won't lie, I know this is a f***ed up situation and wrong on so many levels but I just don't know how to handle it. So about a year ago I ended up hooking up with a friend of mine. We've known each other for awhile, have always been friends...always hung out and stuff...but had never thought about going there. Or maybe we both did, just never acknowledged it until one buzzed night. It was a random, totally thoughtless occurrence. Instead of the one night stand that I thought it might turn out to be, it became a full on friends with benefits thing. So when it's two consenting adults, there should be no complications, right? Wrong! I'd dated his brother before (yes that explains #1 and #2 on my previous blogs) so we couldn't let him find out. My friend "A" had a "thing" for him and to be fair, her and I weren't close friends at the time. We knew each other through mutual friends and she was engaged...but we decided it was better for her not to know either. It's odd though, becuz it wasn't hidden very well so I'm not sure how they can not know. Anyway...next complication, I lost my so called best friends cuz I left with him one night. So that is kinda what complicated the next thing. Confused yet? LOL! Well here goes...my so called best friends were friends with A and that's how I met her. Well they kinda threw her to the wolves becuz she had her own sh*t going on. Then they basically threw me to the wolves too. So her and I started talking more and she and her fiance would go out with me. She kinda knew the story of why our so called best friends ditched me but she didn't know it was him. To this day she doesn't know it's him. It's killing me becuz I don't know how she will react if she finds out. She knows that he and I are great friends but that's the extent that she knows...that I know of anyway. She's never told me anything. Most of the times that she and her fiance would go out with me, she would call him to go meet us also. So when she was around, we weren't affectionate at all. For my birthday I knew they would both be there and I wasn't gonna deal with it so I invited my spiderman to go with me. Well I guess he got kinda hurt that I had someone else there...and I was like hello you had A there and wouldn't have done anything with her around but he claims otherwise. We hadn't been together since Thanksgiving and I'd decided that was for the best for a lot of reasons. But then I saw him a couple of weeks ago and that all changed. She's no longer with her fiance but has a new boyfriend. I just don't know how to feel, how to deal, or how it will affect things with her and me. We're all supposed to meet up tomorrow night for St. Patrick's day...so we'll see how that turns out.