i would say he should eat whatever he pleases, and tell her that as long as he is not forcing her to turn non-vegetarian, she too should respect the same and let him have what he wants. if she finds it disgusting to cook non-veg, as many vegetarians do, he can hire a cook or make it himself. that way, he can assure his wife that she will not have to come in contact with the non-veg and he can still have it, without bothering her.
When one marries a person, he/she should accept as he/she is without asking the other to change. Why should the husband change his food habits at this juncture of his life? He should try speaking with his wife that converting would making him unhappy. She should stick to her food habits and allow him to follow his.
food, clothing, friends, choice of entertainment etc are based on individual decision. her nagging may force him to eat vegetarian but he will eat out non veg food in restaurants. so what's the use of force? it will only create a bad image in his mind for his wife and work badly for his self esteem
When she decided to marry him was she not aware of his food habits? Then why tje sudden change in heart? What one chooses to eat is a personal choice and asking your partner to change his food habits is just not fair. Would she become a non - vegetarian if he asked her to?