How do I cope with the ADHD Partner's emotional instability?


I'm new here! Thank you for stopping by :)

My fiance is transitioning from leaving his childhood home and he is moving in with me (he lived away from their for 13 plus years, then came back home after his separation from his ex-wife)... I feel for him in so many ways. He is not emotionally processing the change well. 3 times in the past few days, we were getting along fine. I presented an issue I was having in the form of "I feel or I don't want to feel as though..."  Twice it was like a dam broke and he threw a fit. He actually threw a grown-ups tantrum. It was more than I'm prepared to deal with. Then yesterday I tried expressing my feelings and he said, "I'm not going to continue this topic, because I've been having a good day..." It was if he cut me off, and invalidated my concerns. I then tried explaining that he was cutting me off... I didn't get anywhere with that either. So the next day he reached out. I had told him that I was feeling as if I can't express my opinion. He said I'm not helping him by pointing things out. I said, 3 things to him. And it all escalated cus his temper blew the roof off.  Every time I try to explain something he is not absorbing what I'm saying or he gives me a, "yeah, yeah, yeah" response. His apologies are worse than his actions, they sound as if he is just saying, 'yeah, so what?"

He told me he feels like his life is upside down and he's losing it. I told him if its that bad he should see a doctor. He said, no. Here I am wondering 2 1/2 weeks before we move in together are we going to be able to survive? When he is frustrated, I try to ask him to slow down. Take a seat, drink some water, rinse his face with cold water and just vent to me. It works to help calm his nerves. But he keeps telling me that he needs me now more than ever... But somehow he also says, I'm not helping him (because of the 3 times we had a snag). The snags he said 1 is like 100x to him. Which I understood. SO I told him I would give him his space to lessen the chances of a snag. That wasn't what he wanted either, said it would make things worse. Before I came around he didn't have health insurance. Later this month he will receive his packet (he recently signed up because I encouraged him he needs guidance that I can't give him and the care of a doctor to help him take charge of his life). When he's great he's magnificent, and I'm in love with him like no other. When he flips out it is out of his control. I try to tell him he hurts my feelings but that makes him upset.

How do you bear the situation before he gets help? I just need non-judgmental advice, my friends don't understand and I don't want my family to think poorly of him.