I’d just go to this event, since you want to go anyway. Like you said, you don’t need his permission, you had asked already and got fobbed off with half-promises.
It is hurtful, but sometimes you need to look at people’s actions rather than what they say. The fact he knew you wanted to go and he just went there without inviting you says it all.
Be kind to yourself, be your own best friend at least for a while!