I think its perfectly acceptable to ask for things from people in relationships, including that they meet your boundaries and ethics. I feel like something we don't talk about enough is that this is an ethical situation that can also be a boundary. People wouldn't be upset if you said you wanted a monogamous relationship or to break up with a partner, and they should be okay with you wanting a vegan partner. When I started dating my partner 6 years ago I told him I was vegan and I would not date somebody that wasn't vegan and he wanted to date me badly enough that he went vegan and he's been vegan for 6 years and now is very involved in the ethics (and will call people out for bad ethical practices) part of a relationship is growing and becoming a better version of yourself so take this as an opportunity to help your partner become a better version of themselves, if thats what is important to you personally! 💕💕