You can't change the mind of someone that doesn't accept when you give them a negative answer. The person who won't accept "no" for an answer tends to feel happier when they get to reject you. The problem is not in your answer, or your will to do some other thing. The problem is with them, not with you. Those who know no boundaries, no honor, no respect are really good at not listening to you and continuing to insist to get their way.
Psychos are especially skilled at that. And that is why it is not your job to change their perception or decision regarding your needs and wants. There are a lot of respectful people in the world who'd enjoy your company and be honored by your presence. So if your significant other doesn't allow you once in a while to do the activities that you like, maybe you'll be better off with someone else.