At a party I saw my bf interacting with one of my ex-friends. I asked him to not pursue her. I found out that they exchanged numbers and he doesn’t see that as a violation cause she pursued him. I told him that if he doesn’t end it I will consider that cheating. He claims that since we’re poly theres no such thing as cheating in our relationship. Also I KNOW she is doing this to hurt me, and that he only wants to sleep with her because she’s [comment about this person’s body] and he’s never fucked a [person with that body type] before.

There’s not really a question here, but here are some truths I can lay down:

One: There can still be “cheating” in a poly relationship. Cheating is anything that violates the agreed-upon terms and boundaries of said relationship. You can tell him that if he does a certain thing, it will be a dealbreaker. He can then, armed with knowledge of the consequences, choose to do that thing. If he does, then you break the deal. If this genuinely is a dealbreaker, then make that clear to him. He is free to be angry or frustrated and feel that it shouldn’t be a dealbreaker, but you get to set your boundaries, not him. 

Two: The semantic argument of who pursued who is a distraction. Is your boyfriend actually confused, in the sense that he genuinely thought you meant “don’t pursue her” instead of “don’t get into any kind of relationship with her”? If so, you two need to work on your communication. If he’s just splitting hairs to try and convince you that you said one thing when you both know you meant another, that’s a huge issue that borders on gaslighting. If this is something he does often, reconsider the health of your relationship.

Three: No, you don’t know he’s doing this to hurt you, and you don’t know he “only” wants to sleep with her for her body type. You are not psychic. Your feelings and fears do not always map to the reality of another person’s experience. If your boyfriend has a history of doing things “just to hurt you,” leave that relationship. If he has said or done anything to indicate that he wants to hurt you, leave that relationship. But if your only “clue” as to his motives is how you feel about it, you need to talk with him more clearly and honestly about why he wants to do this and why you’re uncomfortable about it.

Fourth: While I try not to edit or censor the letters I get, it is cruel and never okay to reduce someone to their body. It sounds like you have an issue with this person, and if she has dome something hurtful or disrespectful that makes you not want her in your poly network, that’s fine. Focus on that. Explain to your boyfriend why she’s your ex-friend and why you would prefer if he didn’t get involved with her, regardless of who initiated said involvement. Don’t insult her needlessly by implying that the only way she could be attractive to someone is if they have a fetish for something about her body that she cannot control.