Help please

I'm 16 about to be 17 my boyfriend is super sweet literally he's the best thing that's happened to me. He and I have been together since we were 11. I know crazy. The only thing is I know he want to have sex. I can tell he's slowly becoming impatient but I'm not ready. I told him I'm not ready and he says it's ok but I know he's upset. what should I? do