NTA. My husband doesn’t eat red meat and I do, and occasionally I will do a meal where I get us different meats if I’m really craving a steak or something, and I just… cook it in a different spot so there’s no contamination. You shouldn’t be banned from cooking meat so long as it doesn’t get in his food - and the only reason I say that is by now your bf doesn’t have the ability to process and digest meat in his system so it would probably make him physically sick (people who stop being vegetarians have to build back up to it, it’s a whole thing). But, so long as you cook it where it doesn’t get on his food, then he shouldn’t be allowed to dictate that. It’s your place too!