How do I convince him to use protection or leave me alone?

OK, he's really immature and selfish. There's no way around that. And there's no way that you can phrase things in a way that is going to make him be any less immature and selfish. He wants what he wants, and doesn't see any reason to change. He's already had every amount of information he needs to convince him to use birth control. He's not doing it because HE DOESN'T CARE. You can either learn to accept this, leave him, or take charge by getting a diaphragm or something like that. Or give him a deadling for the vasectomy. He's not "forgetting" to schedule it. HE DOESN'T CARE.