Advice on how to deal with ADHD partner with RSD

I am looking for some advice on how to handle a partner with severe ADHD and RSD. 
My partner has regular occasions when he is triggered by something I say which causes his RSD and ADHD to go through the roof. It can be something very normal that I say but sets him off and he gets very angry and ends up stomping off to the bedroom or out of he house for hours at a time. I apologise profusely as I try and help and support him even though in a typical non neuro diverse relationship there would not be a problem. It could be something such as not answering him in a full way or not speaking clearly enough. If a friend or family member said the same thing there would be no problem at all. And often he does the same things to me and I look at the situation and think it feels very hypocritical. I am very sad because it is becoming very regular that he goes off angrily and sends catastrophic messages which are very hurtful and upsetting at times. He always says it's his head that's the problem and not me however it is difficult to cope with and I'm constantly in tears. I want to support him by he can be quite cruel. And if I treated him the same way he would not tolerate it and would go wild. 
I need advice on how to deal with his RSD episodes as they are getting more regular and worse. I see him happy around other people and although other people may say things that would normally trigger something if I'd said it, this makes it harder as I do so much on a daily basis to support him. When he is feeling happy he says we have a wonderful relationship and I am the best person he could ever be with but it doesn't feel like we have the best relationship to me. It feels like I am making him unhappy and I worry that we are not that compatible any more. I've read loads about ADHD and RSD and it all fits with the way he acts but it's very hard to cope with the extreme moods. Any advice would be most welcome as I really don't know how to deal with these situations and although I'm always on high alert to avoid triggering him, it would be a relief at times not to be constantly walking on eggshells around him. I do everything round the house and am his carer really which I don't mind but he says very hurtful things and I feel very undervalued and taken for granted. It feels like the hyper focus of our relationship has gone and I'm not shiny any more. I'm just there to do things for him.