How to deal with my step dad? (kinda long sorry)?

The things you described can be seen as very serious, no the eating part but the forcing himself on you, how old were you? You could try leaving and living with another family member for a while, it may be a drastic change in lifestyle but it could be a way of getting it across to your mum how much you dislike him and she may talk to him. There aren't many things you can do now that he's a part of your life but i'm guessing its only a few years till you can leave home.