This relationship ended 5 years ago. They were 19 and 24 when they met. He hasn’t done anything as far as I can tell to make you think he would want to be with her. It’s common and meaningless to search your exes to see what they’re up to. I guess talking about someone when drunk could indicate they might not be over that person, but not necessarily. It sounds like he had some trauma from that relationship that he needed to work through, and sure, I can see him being like, wow, this new relationship feels so much better than that previous one.
And yes it is crazy jealous and also inappropriate to ask him to wait outside so he won’t be in close proximity to her. That’s very controlling and weird.
I think this sounds like you need to work on your confidence.