Marriage.

I've been with my boyfriend for a year & a half & we have a 6 month old. I love my boyfriend to death but every time I mention marriage he doesn't give me a valid answer to why he doesn't want to get married. I cried last night because he doesn't want to. Not yet but I'm ready to do it. We are pretty young 19 & 20. But it's not taboo people in their 80's got married when they were 18 & 19. I'm ready but it hurts that he doesn't want to & im not giving him any type of sexual pleasure until he tells me why. Also I'm scared if I continue acting up he probably won't ever marry me or want to break up with me. HELP