{{Sean}} What they all said. You are no good for anybody if you don't take care of yourself.
Even in a clear-cut relationship (such as, dude, my MOM) sometimes you need to back off and give yourself some breath during a long illness with no end in sight.
So much this. I cared for both my dad and my husband when they were gravely ill and they both had periods of, well madness really. The blessing was that they didn't remember this when they were lucid.
Take care of yourself dear. This is so very hard. Love you.