What was running into your ex like while you were on a date with another girl?

Just looking for others opinions/experiences here...
Been dating this guy who is recently out of a serious relationship. At first he played it off like he was over it but then after a month or so he admitted he was feeling bad about the breakup again.... Apparently it was a bad breakup and it's obvious there's unresolved feels and we had a short falling out until recently.
We were on a date the other day and guess who walked into the restaurant - his ex. He immediately got super awkward, tried to not be seen, didn't really talk to me for a good 10-20minutes (focusing on the game on tv instead), I felt awkward... We got the check rather quickly and decided to go elsewhere. But even when leaving, he was walking like 20 ft in front of me! I felt like he didn't want to be seen with me and I was trailing him like a ****ing puppy dog.
After the awkward settled, I ask about their relationship and he immediately got defensive and like I should've known better than to ask. (i think that's a bit insensitive to me, especially when the date was basically ruined) turned into a huge fight and he told me he didn't want to talk to me. naturally, i pester more and air out the feelings i've held back about the situation, like he treats me like **** basically and has 0 respect for me. His response: nothing. Cool, thanks for the confirmation.
Has this happened to you - dating while still not over your ex and have a run in like this? Did you feel bad for the new girl at all, or were you just so consumed by your ex that you really didn't give a **** about the new girls feelings?


Source.