Ooohhh OP this happened to me once! Have no idea if it will be the same explanation but I'll tell you anyway.
So, was seeing this guy. He seemed really keen, a real gentleman, really into me. Slept with him... Boom, he's ignoring me. He goes home, I don't hear from him for days. Total tone shift. I'm in bits because I thought we were at the start of something.
So, next time we spoke (he eventually replied to my text and he asked to meet up) I broke things off via video chat lol. He was shocked and really upset, asked why, I told him exactly why.
It was a long conversation, but he revealed he had read online that the best way to get a woman hooked on you is to ignore her after sleeping with her when you first start sleeping together. He told me that. He read that somewhere. He only did it because he wanted me to like him more, he thought he liked me more than I liked him.
I told him it was bullshit, I liked him well enough before and it hurt me.
Even if this is the case, definitely chuck him cus it's mental.