I used to say that as a vegan, I would only date vegans. It just so happened that B was also vegan when I met him so that made it easy for me then. However he began eating meat once again earlier than I did. Did our relationship fall apart? Not at all. Perhaps we both inheritantly knew I was not that far behind him, and was making bone broth in no time.
But I do know that some people have strong opinions on this, and regardless, some are in a relationship where the eating habits of one are as far as they can be from the other. Or if not a relationship, either a close friend or family member eats differently to you. So what can you do?