I think this should be in relationships, rather than AIBU.
The way I see it, you were having an argument, tensions were rising, you asked him to leave it, go downstairs to calm down, you thought he'd follow you if you went downstairs, and that he would antagonise you to the point where you would lose your temper. You slammed the door in his face not realising his fingers were in the door, he punched the door and shouted at you.
None of this is good OP, both of you behaved badly, however it's the dynamics, he wouldn't leave you alone, and you knew he would follow you downstairs and antagonise you until you exploded - that's bad, it would probably then be your fault and not his for the way you reacted to being antagonised. He would then get to play woe is me.
He was standing in the door, what would have happened if you did go past him? What would he do?
Asking someone to leave a flammable situation isn't bad, the fact he wouldn't, inflamed the situation. Again bad.
You slamming his fingers in the door, is bad too, I know you wanted to be away from him, but that wasn't the way, but hindsight is a wonderful thing.
I would say you were as bad as each other, but I would say you both reacted badly.
What has happened with arguments in the past? What do you get out of the relationship? Does he antagonise you a lot?
Its sad to say, but I think you need a plan for this happening again, like lock yourself in the bathroom, or go for a walk.
I really do think you should get this moved to relationships, there's some wonderful and wise women on there who can help you.