How should I respond to this guy?

I was talking to this guy and it went south very badly after 7 months. Long story short he wouldn't commit to me. A week or two after we had a fight that ended our situationship, he already started getting with a new girl after he had told me it was going to take forever to get over me... damn two weeks. Anyway, we were at a college Halloween party and I looked real good to say the least. I didn't interact with him the whole party until the very end he said bye to me when he left and I said bye. My bye wasn't very enthusiastic however later in the night at around 5AM he texted me asking me "Did you have a good night". Why does he care to ask me if my night went well at 5 in the morning? Why is he even messaging me or thinking about me at 5AM when he was probably with another girl anyway? I haven't responded to his message, part of me wants to but another part of me doesn't. I want him back but at the same time he hurt me. So I'm confused on how to even communicate with him being in the same social group.

How should I respond to this guy?
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