How should I deal with seeing my ex?

There are two events coming up here where I know I’m gonna run into my ex for sure. One is a show his band is playing in that his best friend invited me to (his friend is lead vocals and my ex is bassist). And the other event is my friends sweet 16 where his band is also playing. My ex and I are no longer on talking terms. I was one of his longer relationships and we had some really deep feelings for each other. Ever since we’ve broke up, he’s gone downhill. I seriously suspect it has something to do with drugs. But anyway, back in Feb we ran into each other at the mall. His best friend said hi to me, but my ex didn’t notice me at first. Then once I walked away his best friend told him I was at the mall and he got all excited and went to say hi and ask how I was doing. Then a couple weeks later I messages him on Facebook saying it was nice seeing him and we started talking again instead of ignoring each other. At that time we definitely still had a bit of feeling for each other, but nothing happened. Fast forward a few months later…I sent him a really long message telling him exactly how I felt about him and that I wanted him back. Then he got it and he was so surprised but he said that it was a good surprise and that we could talk but not to get my hopes up about dating just yet. So we started talking. Like how we did when we first met. Things were going well. Then a couple days later I wake up and log on Facebook and he’s in a relationship. I texted him and said thanks for having it in your heart to give me a chance. No reply. Next day he tells me off and I give him a piece of my mind. And we haven’t talked all summer. So my question is how do I react if he tries to talk to me? What if he tries to apologize? Should I approach him? I’m clueless here.