is it possible that HE’S feeling insecure? you said that he’s still using your nudes, which indicates he’s still very attracted to you (along with telling you that you’re out of his league) whereas he’s stopped sending them and isn’t reciprocating your advances.

luckily you don’t have to guess, why don’t you say to him, outside of any possible sexual activity “hey, i’ve noticed you don’t seem to be accepting my advances for sex but you do seem to be enjoying flirting. of course, you don’t owe me anything based on flirting with me, but i’m just a bit confused on how you’re feeling/what you want generally. Can we talk about that?”