He said if I liked him less, he'd be nicer to me?

What you need to do is deny him sex. He's clearly using you, and you are the one who gets hurt. Tell him NO MORE until he marries you. Stick to your guns. Stop giving him for free what he needs to earn. You're nothing but a rag to mop up his needs. He's telling you what you need to know. Why don't you believe him? This is real life, not a Hollywood movie.