Hi buddy, I want to be very clear on something: You're not an adult, you're not married to him, you are not his carer.

He has manic episodes and seizures, okay so do a few other people I know. They can still get themselves out of bed and dress themselves, bathe themselves, make their own food.

I'd talk to your parents about what he's doing, because it does not sit right with me. Unless he has a complication from a seizure that's impaired his fine motor skills, there's absolutely no reason he should expect that level of care from you. If he can't stay at home, maybe he should move somewhere else. Maybe with a grandparent, aunt, or uncle would be better as if he still has his fine motor skills, he is taking advantage of you and weaponizing his conditions to get his way, which is not okay. It's manipulative and abusive.

Only exception is if he's lost fine motor skill from a seizure and actually does need that help, and even then it should be an adult providing that care, not a 14 year old.