my ex repeats himself constantly - he has a mental illness and didn't want help (repeating is only a small part of it). One day my son and I were talking - the son that is most like his dad. He started putting him down and I said, "you know he is still your dad, I'm not trying to critisize him." Son said, "you know mom, I couldn't live with him for more than 24 hours either." But he still loves his dad."

He was just being realistic.
The other son simply doesn't engage in conversation with his dad when it gets real irritating. He doesn't know what to say without getting frustrated and he's the calmest person I've ever met. He's able to let most people just be themselves.
Its ok. We learn to live with all our own imperfections as well as everyone elses. Or we find a way to separate ourselves from the ones that we can't live with. Life.