OP , I think I understand exactly some of where you’re coming from .Your post has made me post after many years of lurking .I have namechanged for this as connecting to my previous posts, (admittedly very few and years ago at that), could be outing.Anyways ! I can only extend sympathy to you. I don’t know where to begin.Excuse me for my long rant .We’ve been married over 20 years and DH was diagnosed around 4 years ago and is taking medication. My late teen son definitely has it too but a slightly different manifestation as he seems to be slightly more emotionally tuned in. My son’s only been ‘diagnosed’ with Dyslexia thus far , we haven’t bothered with getting the ADHD/ ADD diagnosed. I felt that the diagnosis for my OH didn’t change anything much, other than confirming what I knew anyways- that something was the matter with him.I feel having to deal with him is a death by a million cuts everyday for me psychologically and has been like this for so long, I just didn’t understand what was going on.In theory there are a 3 adults in our household but there is really only one fully functioning person i.e me. The burden of being responsible for everything in the home takes a toll. He is not engaged with anything at home and to me it feels like having another child. To those saying its derogatory to the person with ADHD , I would say I feel demeaned everyday when I have to point out to him that he should be caring towards me i.e his wife and partner of 2 decades, and our son because he is our son! I could’ve said something to him a million times but it doesn’t stick. If I dare to ask him to do anything around the house even if it is something simple, well, expected to be simple for a grown man, I just know now , I’ll have to redo it or pick up after the mess he’ll leave behind.He goes from zero to 60 in seconds in terms of temper. I cannot relate to him as a ‘partner’ he doesn’t know what li’l things bring about intimacy between people who are together and I certainly don’t expect to retire happily into the sunset with him . He is so variable, up and down, I don’t know whether I’m going to get the enthusuastic, puppy like excited person or the grumpy anxious detached and cold person from time to time.I know now that I cannot be sure of anything he utters, he may deny it completely or say the opposite in the next second or in 2 days or whatever.It shreds my nerves as I don’t know what decisions to make sometimes.He has been absolutely hyperfocussed on meditation and yoga the last 2 years .Somebody could be dying in the house, he would still shut himself off for his sessions - it’s soul destroying. I think I hate him may times .I feel that splitting up with him isn’t going to make me happier as I will still have ‘known’ this person and all of the things he has said and done still hurt very deeply.I had some counselling but it’s still down to me to practice stuff.I feel very lonely as its not possible to discuss or have a chat with him about anything, I kid you not.He constantly talks over , interrupts, hijacks the conversation into a sudden unrelated direction. He is very awkward with friends /guests if I invite anyone over.He isn’t able to even offer anyone drinks, I have to remind him repeatedly and the hosting is pretty much singlehanded and exhausting.This makes me less likely to invite people over , not because I didn’t want to invite them back. I feel constantly exhausted and as I’m getting older, it’s much harder to do everything. It has affected my mental well being very much in terms of constant stress.It’s hard to not take it personally and your self esteem not being affected. The number of things that come to most people’s minds automatically but ‘didn’t occur to ‘ him are mind boggling. It doesn’t matter that it may not be intentional , the end result is the same- one feels alone, rejected, buried under the avalanche of work and home , no emotional support, can’t discuss anything with him about our son’s uni , friends, family , work etc as he will usually say outrageous things and it becomes upsetting for both I and DS. I feel because of knowing that dad has ADHD makes me more understanding of DS’s issues- anxiety, inability to act / carry out tasks, no initiative to do anything , even though he is a very bright lad - I know this is not laziness but it certainly comes across as that. Time has no meaning for both of them . To outsiders, my DH comes across as possibly a bit of a character, always making some unusual quips , smiling and sociable person. But for him everyone is treated the same - doesnt matter whether you are the wife, son, next door neighbour, MIL, casual acquaintance.He doesn’t know that one may behave slightly different with people that are not close versus your own family member.He’s friendly to everyone and anyone. He can be fun sometimes in small doses but the constant ‘out thereness’ is bewilering and exhausting to me. My non ADHD brain struggles with that just as his does with all the rules of life, I suppose. We only go on holiday if I suggest it, plan it, book it etc .He’ll just whiz in, smiling his lovely smile, hands in pocket, saying breezily - “where to next? “ as I’m in charge of what to do on holiday too ! I feel very sad at the stuff we’ve missed out as a family because of all this.
I try to remind myself , (not successfully all the time- I’m also only human ) - that he is a person, be compassionate, he can’t help it, the ADHD makes him who he is - sometimes the most open minded brilliant creative, funny person (but most times a very difficult soul destroying person to live with - when I’m repeating myself for a millionth time), but anxious with low self esteem as he knows he’s not behaving as he ought to and has no close friends or family as he cannot keep up with how to maintain relationships - its all or none. I feel sorry for him and as it is lonely for him too in many ways.Sometimes I wish I wasn’t a sensitive person that I am , but rather someone who could shake these things off and go about my life in a happy go lucky way but everything has worn me down after 2 decades together. Im not going to bother leaving now , dont have the energy. I try and do hobbies, try and keep in touch with friends and do stuff with them etc too.
OP you have to do what is right for you, support for partners is non existent, and even saying that you are struggling with a family member who has ADHD brings out people criticizing .It may not be the ADHD person’s fault but it can still be a private hell for the people they’re living with. Thats just a fact, not trying to be derogatory. It’s not as easy as some posters are suggesting , to separate the deliberate bad behaviour from the ADHD. 
to you .Apologies for the warbling very long post.