I was vegetarian when I started dating the man who is now my husband of 18 years.
He ate meat & fish when we met and I accepted that. When we moved in together he chose to eat vegetarian at home on the grounds I didn't impose it and accepted that at his mother's he ate what he was served and when we were out if he wanted meat, he ate it. After a while his mother started serving him vegetarian and not giving him any meat/fish etc which at first he was confused about but just accepted. His mother assumed he had become veggie because that was what he ate with me when they had visited.
Over the years he has effectively become vegan as well. When my diet had to change due to developing a severe allergy to dairy products, he accepted it. At home he ate vegan, at work he at vegetarian and then suffered with snoring issues, runny nose, blocked nose etc and has now ditched dairy of his own accord.
He classes himself as an economic vegetarian. It is his choice and I don't get upset with him for eating fish or meat if the circumstances mean he can't avoid it - some of his work commitments occasionally mean this is the case, but he knows my feelings on the matter and usually chooses to stay away from meat/fish.
I would not consider imposing it on it, and if I had I don't think the relationship would have made it to the marriage stage. People have to be free to choose what they want and allowing him to do that meant I ended up with the man I wanted to marry.
One of his brothers, who eat all sort of meat from pigeon and pheasant to guinea fowl and other such 'delights' has married a vegetarian. They manage the situation quite happily as well. He eats vegetarian most of the time at home but will sometimes add some meat to whatever is being served and is now happy to eat out at a vegetarian restaurant without issue. It has also opened his eyes as to what is available out there, but I doubt it will convert him. However, neither party has tried to impose their will on the matter in their household either and accepted the other person for who they are. They have been married for around 10 years now, so clearly the vegetarian/meat eater or vegan/vegetarian combination can work and does work with understanding.