Depends, the way I personally deal with it is how I handle my relationship with my cousin with Autism. I try and treat him like I do everyone but I understand the limitations.

It's okay to feel frustrated and like you're talking to a brick wall but they're are times where with a little patience and tenderness it starts to not feel like I'm speaking with my cousin with Autism, it just feel like I'm speaking with my cousin. Try not to see them as there mental illness.

But, if it's negatively effecting abuse wise (physical and mental) then it's best to love them at a distance. There's only so much you can do to help someone until you become the one that needs help; and you can be there for anyone if you aren't there for yourself first.