My boyfriend's sisters treat me horrible?

My boyfriend and I are both juniors in college (20 and 21) and whenever I go over to his house or whatever his sisters are so rude to me. Everything they say to me has a sexual connotation (one time i said "i pulled the handle on my purse" and she didn't hear me all the way and was all "dont tell me the muslces you pulled during you know what i dont wanto to know") because they make total accusations about me and they even got one of their friends to call me a whore at a wedding. It's disgusting and I don't know how to handle it. My boyfriend talked to both of them and I got an apology through txt message from one of them, but I just can't handle it. Even my boyfriend's mom does it to me or hints at it (not as much as the sisters). Her son is who I lost my virginity too. My sexuality and what I do in my relationship is none of their business so I don't know why they say these horrible things about me. It really hurts my feelings.