So, I'm a guy with ADHD (came on here to ask a question about TENs machines for my partner, and then got distracted, but this... lol). Was diagnosed in Australia as a child in the 90s, where their approach is a lot closer to the Americans (i.e. it's much easier to get medication).
First off, I need to clarify: does he actually have a diagnosis. I have to ask because there has been an explosion of people who suspect they have ADHD (I blame WFH... ask me if you want me to flesh out that opinion), but don't really. If so, which type does he have. There are three
- Impulsive/Hyperactive
- Inattentive and Distractible (AKA Primarily Inattentive)
- Combine Type.
By the sounds of it, it seems like he has Combine Type, but it is worth finding out from his diagnosis what they think he has. It just helps for you to know what you are dealing with.
OK.... so what did I actually come here to say........ (ADHD brain going off on a tangent again)..... ah, yes.
First medication: he's going to have a hells game getting on it in the UK. It sounds like he has a stable job, and the attitude in the UK tends to be (emphasis on the word tends, the British medical establishment are not as united on this today as they were in the 90s) that unless its so bad that you can't hold down a job, or its causing behaviour so bad that you can't really participate in society at all they're not giving out the meds. That's because of what the medication is: medical grade amphetamines.
Next lets look at some of the behaviours you described. Yes, he's going to be untidy. It's just comes with the territory, and to a certain extent it's creative mess. I'm guessing a lot of things are 1/2 finished DIY projects left around the house? That's what I mean by creative mess. My advice is to try and dedicate a space where he can be as untidy as he wants and contain the mess there.
The doing DIY first thing on a Sunday morning is another thing I can relate to, and totally get. It's kinda a coping mechanism. Sometimes you know you have the energy to do a certain thing right NOW, and you have to seize the moment, because if you put it off for even 5 minutes it's highly likely you won't have the focus then. Gotta keep that momentum.
Anyway, I think the main point of your question was "should I leave him, and if not how do I make this work?". I'm not going to go anywhere near the first part of that, but my top tip for the second: be as direct with him as you can. The reason ADHD gets lumped in with Autism sometimes is that both groups are absolutely horrible at picking up social ques and subtle hints. If something annoys you, tell him. If he keep doing it (because he will forget you told him) tell him again. The message will sink in. He needs to see that the things he is doing to annoy you have consequences (even if that consequence is just you being annoyed at him for 5 mins).
Let me know if you have any questions from the perspective of someone on the other side of this.