It is reasonable to feel as you do about FIL. He’s earned you dislike. As others have said: focus on supporting your husband. NEVER EVER let the thought that you won’t be unhappy when FIL dies slip out to husband or his family. If your husband voices the thought that he might not be totally sad when his father dies, assure him that this doesn’t make him a bad or unempathetic person, that he has reasons for mixed feelings.