hi there,
I hope things are calmer now. Shame and guilt are the worst enemies for BPD people, together with fear. He felt judged and exposed, and as someone has said, the anger needs a target, and that falls onto us. It takes a lot to know this, and let the anger go past over us and not affect us. I don't know if it's possible.
I reminded him that paint drying too slowly makes him too mad, and every relationship he's ever had triggers anger in him.
Did this worked? That sounds very invalidating. It "blames" him. It would be more shoothing to say "All couples feel angry in moments of stress, and all project anger on each other, it's not pretty but it's just normal human behavior. " There's a joke out there : "Honey, should we go to Ikea or should we just argue here at home?"
It's not only pwBPD who are angry without reason with their partners. And certainly it's not only your bf. So as long as you comunicate that you don't like that, and that you don't approve, you can normalize this behavior a bit. So looking for the cause of his anger towards you doesn't obsess him, and doesn't work against you.
Good luck!