If a guy always wants to talk about sex..is he not into you?

i had a huge crush on this guy for awhile and finally got the nerve to start talking to him and we had bee talking like seriously for about a month then he started wanted to talk about sex and sexual things which hello he'd a teenage boy I'm not dumb.. but I've done things with guys before and he hasn't done anything sexual with a girl before so I know he's just really curious.

but now I feel like its the only thing we ever talk about and he tells me he likes me and all that but I just really feel like the only reason he likes me is for sex.