Just my 2 cents here, but a relationship is 100%/100% so when you ask why it is hard for people to understand and why should they have to, well it's because when they choose to be in a relationship, they need to make the effort as well to understand your foibles and work with you as much as you need to make the effort to overcome those foibles.

Maybe to make it priority you could set yourself a reminder on your cell phone or something? It's easy with ADD to get hyperfocused on something and forget to make that effort, that's just part of the illness, so maybe try to find a workaround.

Finally, I think the key to making that effort and getting the time to prioritize your relationships is to be completely forward and ask for help. Your partner can be part of that. Let them know that it's okay to say, "Hey, can we focus on us for a little while, I'm feeling a little neglected." Or something to that nature. Don't fight and blame yourself, instead try to be more outwardly focused and work with your partner and MI to find the best possible way to make your relationship 100/100.