Me and mine both have issues. He has been dx'ed with mild Asperger's and though undiagnosed he fits every symptom of a narcissistic borderline. I have been dx'ed with schizoid PD and bipolar I, so it's pretty obvious for him when I get manic.
We seem to do great together due to how our mental health situations are so similar yet different. We both use lots of patience when the other is being very difficult, because we each know the other will have to do the same later.
My schizoid anhedonia + bipolar craves stimulation. We're both hermits, so his quirkiness doesn't get too crazy for me to deal with. His borderline gets along with the fact that he knows I have the patience of a saint and won't (his words) "leave him for all the forever times." The NPD gets annoying, but he accepts critique well, and I know I'm egocentric...hence I can't judge too harshly.
When he gets into very over-dramatic borderline states, I can easily talk him down in a calm manner, and he's very good at talking logic into me when I get delusional/paranoid. He likes being over dramatic for his own attention, but quickly diffuses my nonsense quickly.

I dunno. It seems to work for us either way.