10 points to first answer! Why was my friend acting strange?

Last Saturday night, a friend of mine was playing a show at a bar downtown and invited me. I went, and we stayed until Last Call. We went back to his place to watch a TV show he told me about, and at the end of it, he asked if I wanted to hook up. I said no because I have a boyfriend, and he respected that. I crashed on his couch and left the next morning.

Throughout the week we have texted a little bit because we exchanged numbers a few nights before his show. We will hang out again soon but haven't made plans yet.

Last night I unexpectedly ran into him at another bar, where he was sitting with his ex (whom he's still friends with), a friend of hers, two of my friends, and me.

In contrast to last weekend, he didn't say a word to me. Because of it, I felt awkward, so I didn't interact with him either.

His behavior was surprising. What gives?

I've known him for a few years because we have mutual friends and have hung out together with them. However, we have only hung out one-on-one once (last Saturday). He is friends with his ex, but I hear they won't get back together. I'm not sure if they are intimate anymore. When we text, it's is about work, weekend plans, etc., so nothing sexual.