It's mostly about consent. We can debate when and where sentience begins, but it begins somewhere and vegans hold a moral philosophy that says using another sentient being's work product or body without their consent is immoral.
Note that I am not vegan myself but understand, if not agree with, their moral position.
And as another reply said, most vegans recognize it as a "best effort" philosophy, as they appreciate the impracticality of an absolutist stance. They are focused on "harm reduction".
This hits really close to home. Am going through my own divorce right now and my ADHD is a major contributing factor to the breakdown of our relationship.
I don't know about your situation, but my wife has too much of her own trauma to deal with my bullshit (and I say that knowing everyone has their own flavor of bullshit). She grew more and more discontent, and her trauma responses in particular were not a good fit for my ADHD
The "mental load" issue is hard for us, because a lot of the time we just need help learning or noticing. When you start collaborating on those things early it keeps the stress from reaching critical levels. But if the stress has already built up, it seems almost impossible for us to carry enough of the load on our own to bring it back down
I would ask my wife for accommodations like "if the laundry needs doing, leave the hamper in the hallway where I'll see it every time I walk by". Or "let's do the dishes together, or even just body-double for me, because doing stuff as a team is motivating for me and gets it done immediately." But by the time we realized what I needed, she was already too stressed out to see that as anything but "taking care of me" or "being a mom." It hurt like hell to now what I needed and have a partner who was unwilling or unable to provide it.
As the issues grew, our intimacy declined, which made me way, way worse and feel like the woman who already struggled to speak in my love language (unrelated to the ADHD stuff) couldn't provide what I needed anymore either.
I don't mean to trauma-dump, just commiserate. I feel your pain on this, deeply. I think people like us need someone to understand what they're getting into up-front so we can do the work together that keeps it from becoming a serious problem :(