Me (17M) and my girlfriend (17F) have been dating for around 4 months now. She's my first girlfriend. A few weeks before we started talking (not dating) she slept with my close friend. It wasn't a relationship at all, it was more of a one night stand. According to my girlfriend, my friend was bipolar towards her and "fucked her whole dynamic up" and was one of the reasons she had a hard time trusting people again. Apparently, my friend was not over his ex and used my girlfriend as a way to get over it. After they had sex, my friend left her. She tearfully revealed that they had sex around 1 month into the relationship.
I was shocked. Because I originally assumed that they had talked for a bit but nothing more. Also by the fact that my friend treated her like that. I talked to my friend briefly about this (he never revealed that they had sex to me). He said that he never told me because he didn't want to ruin things between me and my girlfriend and also the friendship. My friend has always been there to support me in times of hardship for me and likewise. We're both on the wrestling team and we've won and lost together all throughout high school. Since then, me and my friend have never been that close.
Obviously, I was upset and jealous because this happened around a month before we started dating. She reassured me and said that she was fully moved on and only loves me. And she's been an amazing girlfriend. I love her.
One time, we had a serious argument. Insults were thrown both ways. She was considering breaking up. She said, "The fact that you two are still friends is… I don't know" and seemed really upset about that fact. Originally I said "You're right" Since then, me and her have made it up but it came up recently. I asked her, "do you mess with me and him being friends?" She said , "I don't care", but was obviously upset.
I'm really confused what to do. I know I originally said she was right. But me and my friend are in the same friend group so I can't avoid him. We're also obviously gonna see eachother during practice. What doesn't help that us two are leading team strength and conditioning this year so there has to be a level of collaboration. Plus, she also made the conscious decision to be with him for a period of time.
I'm really conflicted. I don't want to choose between a friendship and a relationship, especially if it was something I had no idea that happened. I'd really rather keep both, when both have helped me so much. Part of me feels really bad for still being friends when he treated her like shit. Another part of me is shocked that my friend would do anything like that. And part of me is confused because I didn't know anything about their relationship when it happened. I haven't talked to my friend in depth about this yet. I will to understand why. I truly don't know if I'm being a bad person or not.
I know I'm immature and inexperienced in relationships. I'm only 17 years of age and have been dating for 4 months. But I want to handle this relationship the best I can. Our relationship has been great for 4 months and I don't want the solution to this problem to be "Just end it. Run for the hills. She's not good for you" when she's been 100% loyal.
TL:DR:
My girlfriend is upset at me for still being friends with her ex, which treated her poorly. Me and her ex have been good friends for a long time, longer than I have been dating my girlfriend. I can't avoid him because we're in the same sports team and friend group. I don't want to choose but I may have to. What should I do?
thank you.