OP I've read your posts, but not all the other responses.
I stayed in a relationship for a longer time than I should have because my ex has autism. I used the same reasoning as you: his brain works differently, it's a disability so he can't help it, plus, look at what he can do rather than can't, focus on the positives.
These are all correct ways to look at it when the emotional dynamics and mental load are more balanced, like in a friendship.
But you're in an entirely different sort of relationship, one where what people experience in interactions with him outside are in no way mirrored with what happens behind closed doors.
The bottom line here is you. You need to prioritise yourself. You're talking a lot about him, explaining his way of thinking. It's a form of justification. In a friendship that's ok. In an intimate partnership it acts as relegating your thoughts and feelings to second place. You're adapting for someone else, which is normal in an intimate partnership, but when it's only you, all the time, it's not healthy for you.
You're asking what other relationships with income disparities do, yet that's a false comparison, because of the reason behind the disparity.
You are allowed to put yourself first. You're allowed to not be married to someone who doesn't make you happy. You're also allowed to want a partner and not be a (mental) carer. It doesn't make you a bad person at all.
He's not more important than you because he has ADHD and a worse childhood than you. Neurodiversity isn't a trump card. People don't have to accept being hurt by another person because s/he is neurodiverse, even when the neurodiversity means they do not realise or intend they're hurting someone until it's pointed out. And especially when that's a pattern over years that the person can't or won't alter.
The bottom line is that you're not compatible. What you both want, expect and need from a real action ship appear to be different. That's ok. It's ok whatever the reasons and whether one partner has severe ADHD, or not.
The gym membership is not the real issue, the income isn't really the real issue. You're afraid of facing the real issue head on, so this is a stand-in. In the long term, it's just wasting your time.
Every time you find yourself making an excuse for his behaviour in your thoughts, make an excuse for yours too.
Put yourself first in your mind, because he's first in his. The reason for that deserves compassion but the reality is that if you don't focus on your needs, they simply cease to exist in the relationship. You need to advocate for yourself in your own head, because right now you're advocating for him every time you justify his behaviour. I know he can't help it, but that fact doesn't outweigh your right to get your own needs met.