Undiagnosed adult, need to talk to partner abut going to GP

To be clear I am not diagnosed, but have been doing research the last few months after meeting a female colleague diagnosed Asperger's and realising we experienced life very similarly. I'm starting to think I want to pursue a dianosis but I haven't discussed this with my partner really because I struggle unless I write so i can edit in a way that isnt half backwards (I'm the worst storyteller/messenger I know). I've talked about my findings but struggling to take the courage to relate them to me personally.

So today we got on eachothers nerves. I get utterly overwhelmed with form filling, online booking, purchasing (say filling tax forms, passport forms, buying plane tickets which we do a lot of as LDR atm etc) which makes me VERY slow at such things. He is blunt with me when I'm getting stressed. He reassures me he understands I find these things difficult, like I still haven't finished a short email to my mother-in-law that I started 4 hours ago difficult. But it feels like he starts rushing me or getting frustated which speeds up the inevitable of me snapping at him. I feel terrible when I've done it. But in the moment it's like, I cannot express why I'm frustated in general or specifically with him. Sometimes (but not always) the words are there, but they won't come out. Obviously he then rightly is upset that I snapped when he thinks he was helping by pointing something out my muddles brain might have missed. But it just feels like I'm being treated as stupid or lazy or exaggerating because I can't really read his intent all that well especially if I'm  overwhelmed already.

I don't want these kinds of avoidable issues to wear us down. I know I have to discuss what's going on with me, I'm just terrified of him being dismissive. He's very supportive but I'm so bad at talking and I get discouraged easily, if he asked why I think I might be I'd easily just end the conversation with a 'nevermind maybe i'm wrong' and pretend it never happened instead of persevering. He's maybe experienced one true meltdown after an awful GP appt where I was dismissed as being the cause for my chronic inflammatory skin condition, and I was particularly rude to him then too when he suggested I process this calmly and I yelled some choice words about this being how I process things. The closest I get to talking about my possible want for diagnosis is my saviour sentence 'MY brain doesn't work like that' which barely scratches the surface tbh

My question here is how do I bring this up? What did y'all do when you started seeking diagnosis