He probably wanted a relationship with someone who was more experienced (or at least more willing to reciprocate the feelings he has - ie hornyness). It probably sounds a bit harsh, but at his age he probably wants to enjoy all aspects of a relationship, not hang around waiting for you to be ready to lose your virginity. So hes gone cold on you, because you aren't who he originally thought you were.
Edit: As for saying he was fine with it, he probably thought he could persuade you to have sex (which is why he suggested valentines day), as you've ruled that out, hes probably realised that he doesn't want a relationship with you.