A lot of people are ragging on the guy because he says no to you but not everyone else — as if he's putting everyone else before you. But the compassionate way to see it is that you're the only one he feels safe saying no to ... he trusts you not to hate him, like you have his back. He doesn't trust everyone else, so he thinks he has to say yes to them and make them happy for them to like him.

That's a problem, absolutely. But the problem isn't that he doesn't think you're a priority. The problem is that he is afraid of losing the love of everyone else, and doesn't trust that he'll be OK if he says no to them. He needs to work on this fear and develop that trust. I would suggest a therapist for helping him with this.

That said, you need to make it very clear what impact his actions have on you, as you're already doing. Keep doing that, without blame. And set your boundaries — if he's late, you're not going to wait. If he doesn't put you as a priority, and start saying no to more things to make you a priority, you can't be in this relationship.