Saw my ex after 8 years

I ran into my ex and his wife yesterday at Dunkin. I noticed her first and then realized he was there. I went into panic and called my husband and stayed on the phone with him until my coffee was ready. While on the phone with him my ex came up and said “hey, how’s it going?” I just said good and gave him a look and got my coffee. We haven’t seen each other in 8 years and were together for 5, very abusive (verbal, emotional, physical, and at the end sexual). Why would he talk to me? I left him and want nothing to do with him. Why would he come up to me? What’s the fucking goal? Why would I act happy to see him? I feel like that’s what he expected/wanted