My boyfriend is still really good friends with his former fuck buddy and it makes me super uncomfortable. How do I deal?

My boyfriend and I are have great communication in our relationship. We are always very open and honest with each other, which makes me trust him and puts me at ease. However, sometimes he tells me things I'd rather not know. For instance, yesterday he told me that he and one of his best friends used to sleep with each other. He and this girls are still good friends and I hate it. It's not that I'm afraid he'll cheat on me or that she'll try to sleep with him again (she has a boyfriend) it's that every time I hear her name, I picture the two of them having sex and it makes me feel like somebody kicked me in the chest. From what he tells me, she seems like a great person and I think if he hadn't told me that they used to bump uglies, we could be close, but I just can't shake this rotten feeling. I feel bad because I'm friends with a guy I used to fool around with and he is completely okay with it, while I on the other hand don't like for him to do the same. It's so hypocritical. How do I feel better about my boyfriend's friendship with this girl? He is the best boyfriend I could have ever asked for and he goes out of his way to make me smile every single day, so I really don't want to let something like this ruin it.
My boyfriend is still really good friends with his former fuck buddy and it makes me super uncomfortable. How do I deal?
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