<human>: Can you give me the gist of the text in a nutshell?

We were together for over three years when things started looking like they weren't going to work out. Technically, I broke up with her although the feelings were probably mutual about splitting up. There was the whole "I hope we can stay friends" deal going on, and that was that. I thought I was going to be ok. 

I find out that she slept with another guy (a guy she's had her eye on for quite awhile) very soon after we broke up. This crushed me, even though I should have had no reason to be mad - we were both single now, right? 

This all seems like normal post-break up stuff that one will get over with time, but it doesn't get much better. Not too long after that, WE slept together again because we were both feeling it. I thought, "Hey well maybe we can stay friends with benefits if anything."

The problem is that she doesn't really talk well with anyone else about relationship/sex/personal stuff, so I get to hear all about it, including about the times that she has sex with him. And since that night we slept together, there has been little intimate interactions between us, with her reason being that she just thinks a lot more about the other guy she's also getting with. 

I didn't think I'd be this jealous. She tells me about how much of an animal she becomes in bed with him, and I feel terrible when I can't get the same reaction out of her anymore (We hadn't been doing well in that department toward the end of the relationship). 

I wish I didn't feel this way. I wish I didn't want to feel wanted by her in that way, but I can't stop thinking about it no matter how hard I try. 

I know I should probably just cut contact, but my mind wanders too easily, and I know I'd be worrying about what she's doing with him at some given moment. 

I could really use some advice on what to do. I don't want my thoughts to be constantly occupied by this issue.
<bot>: Broke up with ex, she starts sleeping with another guy and tells me about it because I'm her "best friend," I'm jealous that she doesn't feel that way about me.