Am i free to leave if i cant stay with my husband?

My husband is a UK citizen. i m not. I m from Bangladesh. we live in the UK. Our mariage is not happy. I feel being used. I want to leave him. But the problem is he is having a critical ilness and i m the care taker. he can do his work alone but he needs a care taker. he threatens that if i leave he ll ask the police to catch me. can he do that? are there any organisations which i can get help from. Am i free to leave if i dont want to be with him anymore?