I ended up just ignoring his facebook messages rather than potentially adding fuel to the drama.
We had the big weekend event last weekend. There are a lot of mini-events within it and luckily we weren't in any of those together so we weren't forced to interact. When I saw him around during the rest of the weekend I just continued to not acknowledge his presence and while I got the impression he was trying to catch my eye, I never made eye contact and he didn't make any attempt beyond that to interact with me.
Hopefully this will be the end of it.
Also to the people who said calling him my ex was a bit of a stretch, you're completely right. I've never used that term for him in my real life, and I really should have put quotes around it in the title of this thread