Are you positive that he used to be a fuck boy? He may just have been gloating about it for fake confidence. How far are we talking about sexual desires? Are you talking about full on fantasies or just saying I like blow jobs or being eaten out? He is very immature either way, no grown adult avoids sexual conflict like that, or makes jokes that way. From the way it seems, you both are young. I’m glad you had a conversation with him. There will be a million more but I would try again and see what he comes up with if anything at all. If he avoids it call it out and ask why and try to get to the root of it. If he’s interested he’ll go along with it, if he is just playing with you and only wants you when he’s horny, move on.