How can I feel better about stopping therapy right when I want to be there?

Your dad is right. Your mom sounds to needy. This is not good for you. Being there for your mom hand and foot is like bringing world peace. IT JUST WONT HAPPEN. Just cause your mother is unhappy doesn't mean you should to. Cause in the end you will have a kid and no partner and start a whole new cycle of resentment. So please fix your self and go to therapy.