FWB her or me?

Okay, so I am in FWB relationship, he is my Dominate and I'm his Submissive. He tells me all the time how I am his, he owns me and etc. I don't have an issue with that. Then he tells me he is going to try to have sex with another girl. I have told him, if he does that then he isn't fucking me. He can be FWB with her or me. The thing with her is, she has never had sex, so he would have to teach her EVERYTHING. His reasoning is "she is attractive". He can have me when ever he wants to, he has not only claimed my pussy but he has claimed my ass as well. He ties me up, whips me, spanks me, chokes, bites, etc. If I were to fuck or even imply I was wanting to fuck another guy he wouldn't be okay but I'm supposed to be okay with him wanting to fuck another girl. Not only that but I don't know if she actually hasn't had sex and I'm not going to put myself in a situation where I can get an STD. I'm not sharing my Dominate. I don't think I should have too. You have decided to make me "your" submissive. I'm not going to any other dominates and asking them to bite me. What do you think?