I've been with this girl for about 5-6 months. Things have been going great. I have no complaints about the relationship, and it is in fact one of, if not the, best relationship I've ever been in. I'm 27, so I'm at least old enough to realize that this is in fact a very good relationship and that it's not just the head-over-heels feeling you get all the time when you are 16.
Now for the problem...
I recently found out that one of my really good friends (we'll call him Al) had sex with my girlfriend (we'll call her Sue) in a bathroom at a party that I was at a few days before we got together. Al has a girlfriend that he has been dating for 3 years, but Sue didn't know that at the time.
Sue also made out with Al at a party Al and I were both at soon after we both met her (we met her at the same time).
This happened right before we started dating, but I just found out about it now.
During our relationship, Sue and I have been very good friends with Al and his girlfriend (I have been for a long time), and have hung out with them often.
My issue is basically three-fold:
1) I am extremely jealous, because I think Sue actually liked Al the most, and I highly doubt we would be together if Al didn't have a girlfriend. She assures me that this is not true, that she liked me the most the whole time, and that she only hooked up with Al because she was lonely and craved the attention (she's on medication for depression). They were also both quite drunk, and this is another reason she states.
I'm not sure that adds up. I was at both parties, and if she really liked me the most, she would have spent her time and energy flirting with me. That's what I have always done if I've had a huge crush on one particular girl and she was at a party I'm at.
2)I can't believe she can so easily shrug aside the face that Al cheated on his girlfriend with her and become friends with him and her. She feels no real obligation to tell Al's girlfriend what happened even though she considers themselves friends.
3)I can't believe I have the type of girlfriend that has sex in the bathroom of a party with a guy she barely knows.
Some may say that maybe she's cheating on me with him or with someone else, but I know she's not. That's not an issue.
I've been really upset about this and we've gotten into several arguments about it.
Given the fact that our relationship has been nothing but great, am I being unreasonable for getting this upset about this? I found out about it roughly 3 weeks ago, and we still have an argument about it every few days, always prompted by me. Am I being unfair to her by constantly questioning her about something that happened before we officially got together? This girl really loves me and treats me well, and I really love her, and I don't want to lose her over petty details, but I'm not sure how petty these details are. It's hard for me to be objective about the situation, so that's where everyone else comes in.
Thanks to everyone who takes the time to read and respond. I really appreciate it.
(I plan to make whether or not I should tell Al's girlfriend that he cheated on her the subject of another post. One issue at a time.)