She supported you through a childhood trauma. Ok fine. That's what a good friend does. How long do you have to keep paying her back for that. That act of friendship being a reason why her behavior is ok taints it and makes it into something ugly. Being a good friend once doesn't give her the right to be a douche now.
Even if he'd been out as poly, his behavior STILL would have been dreadful because he should have been at the hospital supporting you. He let you down and you have the right to be angry about that.