He has used you. I don’t agree that it’s just a mismatch in what you wanted - it’s perfectly possible for him to make clear he wants casual if that’s the case and for his behaviour to be consistent. Instead he chose to lie by presenting himself as something he wasn’t.
It’s not your fault OP and I think this is really common. I’ve even heard men excuse this as a biological thing that women won’t understand - they’ve involved to have sex then leave and find someone else to impregnate. Delightful.
I find it very disturbing that someone can put on an act so easily and then just drop it. It’s not just that they’re being a bit more distant. Men like this often become so cold that it makes me feel they don’t even see the woman as fully human - just an object they’ve used.
However I actually think he’s done you a favour. I think men like this often have a certain kind of attachment style which is not conducive to healthy relationships. Why would you even consider continuing with someone like this? This is the point it should still be exciting and texting each other all the time. He’s had sex with you, refused to even look at you after and not been in contact since.
Even if someone did just want casual sex, and some of the excitement was gone once it was over, a normal person would still be respectful and polite the next day. I mean, I am nicer than that to acquaintances at work. Never mind someone I’ve been texting constantly and then had sex with.