This! Not only is this not your responsibility, its not your problem either. It's his. My mother has blown up at me in the past. (I think she might have BPD.) It's part of BPD. My dysphoric mania plus her BPD = disaster. I hope you can keep your distance and that he doesn't go on a rampage after your email. (I don't know what your email says, but I'm sure it was a rational, well-thought-out email.) You sound like you're doing well.