In Writing Magazine, Judith Spellman reveals that best-selling crime novelist Michael Connelly had a day job and wrote in his spare time and that put a strain on his relationship. But he made a deal with his wife: he would write four nights a week, usually from 10pm to 1am plus one weekend day. The other nights and weekend day he'd stay away from the writing desk.
If you're a spare-time writer, it may be worth formalizing some deal like that to avoid your writing passion from interfering with your relationships.
(If you need some help with your writing, a great starting point is my book, "Your Writing Coach," and the free materials at www.timetowrite.com )