Only one trying to save my marriage

I am a non-ADHD spouse married to an ADHD man, we have had our share of issues but I am wondering how I can better keep the peace. I am currently a graduate student & mother to 3 under 7yrs old. My husband feels no need to help lessen the load on me and it seems as if his interest is everything but our household. Another issue we are currently facing is that I have to manage everything in the house (appts, paying of bills, shopping, etc.) and when I make a plan for us (because he just won't) he always abruptly changes plans to do what benefits him and then we argue because he seems to not remember or has twisted the initial conversation to fit what he wanted. This makes me insane to the point that I will write down what I said or text it to him for proof later that it was him and not me. My husband always commits to helping around the house but hardly follows through without me having to ask him several times and a lot of times it turns into a war because it can be a week (or more) later and the chore still will not be done. I do not know if this is an ADHD issue since he seems to perform just fine at work. I have had to beg him to take 2 days off (or else he will work 7 days with no additional pay) as he works on cars (which is also his hobby) but he feels like even when they are closed he should be there to work on his hobby (car) as he put it, despite me needing help at home with the children as well as around the house. Also, I started grad school before his job so he knew my commitment usually required 40-60 hours of research per week (not including semesters I take class) but then decided that his wants were more important. I don't mean to sound like I am bashing him but truthfully, a PhD in a science field is what is going to carry our house and hopefully if he decides to, put him through some sort of schooling. I don't care about him going (or working on the car when it is home) the issue is that he does that FIRST and then always FORGETS his responsibilities at home. Instead of being home on Monday, like we agreed, he decided himself that he would go all day (8-5/6) and work on his car all day. This time could be used to help me with things like grocery shopping, cleaning around the house or a day-date where we don't have to find a sitter. My husband is irresponsible with money (spends on what he wants and has over-drafted the acct), impulsive with money, refuses to follow-through on anything other than his likes in life and really selfish. I do not know how to deal anymore.