What would you like to ask?My boyfriend says that there's a dangerous animal protien in cheese...?

I'm being serious, he says that there's something called Rennet Casein in cheddar cheese. I'm trying to ween myself off cheese (btw I'm a vegetarian, not vegan, just veggie) but it's very hard. It was easy not eating meat, not drinking milk, or eating eggs, or butter. But I can't go completely vegan for some reason... I just can't make myself not eat cheese. Why? (BTW I know that Rennet is the lining of a cow's stomach, and I really don't want to eat that but i love cheese so much)