Before I type anything else, I want to point out that I am just spit balling ideas here. Since Brandon is gay, the whole candle for you idea can be sort of ignored. But only sort of. Let me be clear, after writing all of this down, none of it excuses his behavior.

There are a couple of things that could explain this behavior. While he might not love you in the sexual sense, if he has been, or considered himself, the most important male presence in your life, it may be that he feels that your husband is some how replacing him. Mainly this is due to the fact that he declined a place in your wedding party and seems to be doing so again. Perhaps the wedding makes it 'too real'.

You also mentioned that he is back in contact with his father. It could be that this has depressed him and he doesn't much feel like celebrating. For this, however, my concern would be twofold. That he would be withdrawing would be worrisome as would his inability to speak with you about it.

Regardless for the reason, my gut feeling is that your friend is doing this because he is an asshole. The disrespectful attitude, the lateness, the attacks on your designs, all point to a guy that does not treat his friends well. You have a wedding and future to plan. Don't waste anymore time trying to include this guy in either.