My boyfriends female best friend is trying to befriend me but it's possible that she might having sex with my bf but I don't have proof so I don't want to talk to her

I don't want to be rude or blame her for something she didn't do, but I just don't want to talk to her because my boyfriend and I had a fight because of her a few times. It's a long story but he says she's a good friend and I agree she is but they are very close and what they talk about is usually sex. Don't judge me but I think a guy who has a gf shouldn't talk to some other girl like this. Their friendship is older than our relationship that's why I don't want to be a dick and tell him that I don't want him to talk with her. But I caught him lying to me when he meets with her. And one other thing is he made some of her "hot" photos his profile picture. Like I'm his gf why he put other girl in his pp. She is a kind of person that could have sex any random guy and I'm sure she never cares sending nudes to her friends etc. So when we had a fight with my bf I called her a whore with anger. And now she's texting me and acting friendly, I don't want to share my feelings with her but I don't want to ghost her too. I don't know what to do with her. Maybe I should share my feelings and tell her to leave us alone. I really don't know what to do. I know this sounds complicated and I sound like a freak but please give me some advice without judging the situation. I tried talking with my bf but as I said he keeps seeing her and lie to me. When I caught him he said he had to lie to me because I suspect and there's nothing to suspect, they just hang out as friends.