Girlfriend plays on a team with the guy that she cheated on me with

My girlfriend and I have gone through a tough year. I broke her trust and her heart by continuing to speak to my ex (of 10 years) about the possibility of potentially getting back together at some point in the future. She found this out by looking through my emails and phone. This made her cold, and lose trust in me. In reaction, she began having an intimate relationship with a close friend (sex, but also romantic feelings). I soon found out about this, and in the end, we made the decision to work through it all and start fresh. Starting fresh meant no communication or friendships with any of the people that caused our relationship pain.

Just recently, she and I found out that the close friend she cheated on me with will be playing on the same recreational sports team with her. I've asked her to play on a different team or have him play on a different team. She is unwilling to do that, and says that if she can't play on this team, she'll quit the sport altogether, which is one of the most important things in her life.

Should I be ok with her playing with this guy? Am I being unreasonable to force her not to play on this team? Or is she being unreasonable for playing on a team with the guy that she cheated on me with?

I'm really at a loss, and don't have many people I feel comfortable talking to about this. So I figure anonymous perspectives could be helpful.

Thanks.

You can't force her to do anything. She's bending the rules by saying she won't play for another team imo, but I'm assuming other variables are the reason she wants to be on this team and not that guy... right?

It would be unreasonable to demand that she gives up "one of the most important things in her life." Let her have that. You trust her, right? Then set some boundaries, like only interacting with him when it's necessary to the game, and trust that she'll stick to those boundaries. If she doesn't, then bail.

B0ll0cks to that, i wouldn't be happy about it. How would she react if you were playing sport with your long term ex? I bet she'd hit the roof.
Remind her of the hurt this has caused, ask her how she would feel if the situation was reversed then see what options are available.

Personally speaking, i would not be happy about it!

You cannot force her to do anything, but if she stays on that team, you can break up with her. It's important to you that she change to a different team, but she doesn't really care what you want, does she? Now you know she doesn't care what you want, how do you think this can continue long term? The main reason she wants to stay on this team is she wants to be around this other guy she likes. If she didn't like the guy, what's the problem with changing teams?