WIBTAH if I rejected a friend that I've been staying up with and talking to
I (f23) have befriended a guy online around 2 weeks ago. We have been staying up late together chatting about random things and sharing stories with each other. I tossed like two funny flirty lines to him in those days, but it didn't seem like he was interested (besides ruining his sleep schedule to stay up with me). We have not talked about anything sexual either. We have both been broken up from our partners around the early months this year, so it's clear that both of us enjoy each other's company.
Today I woke up to him sending me some pretty obvious signs that he likes me and is flirting with me. But I'm thinking of just asking him if we could remain friends. He is a nice guy, I enjoy hanging out with him. I just feel like I would be the AH since I have been staying up really late talking with him and because I kinda flirted with him at the start.
EDIT: For clarification I AM going to reject him, I just wanted to know if I was the AH for doing so. I'm not asking for help with the decision part.