Nail him down for the next date
Your goal is to get a date with him before he goes to Vegas. Looks like you've agreed on a possible date on Wednesday and probably for only a short period of time. Not the best situation to be in, but he's not giving you much to work with.
I'm also a bit confused about your ultimate goal with him. If he just started acting weird after meeting his ex and he's going to vegas in a week, he doesn't sound like someone looking for a relationship. Maybe you just want to hook up?