I think theatre helped, only because it was acting experience. I got to work with a lot of directors.
I think sometimes we look at other people's marriages and we think they must always be so happy together. I don't know anybody who's married for a long time who hasn't somehow made room in their love story for the hate and resentment that they sometimes feel toward each other.
Writing has laws of perspective, of light and shade just as painting does, or music. If you are born knowing them, fine. If not, learn them. Then rearrange the rules to suit yourself.