Advice, please?

I'm engaged and have been for a while. We recently transferred to a new college together and since then I just haven't been feeling the relationship. The sex isn't great, the fights are stupid, and I feel like we aren't wanting the same things anymore. I've recently become a vegetarian, as I have wanted to do since I was young but the lifestyle was unsustainable, and he refuses to get over it. He says he won't ever be able to cook for me, and refuses to just leave meat out of recipies, or even set my bowl aside before putting the meat in whatever it is. I live with his brother and go to school full time while working to put myself through school. His dad pays for everything and he refuses to do as his dad asks because he is stubborn. We are 20 and 21, and I suffer from manic depression and anxiety. I can't tell if I'm overreacting or being ungrateful or what. My brain is a mess. We have a cat together, who makes me so unexplainably happy and if we break up, I may lose him since my name isn't on the adoption papers. I love him and he has been nothing but good to me. But I tend to put others before myself and question if now is the time to make my own decision. I would like some advice. I am going back to therapy soon, but I have a few days until then. I just want some advice.