Our minds need to develop new thought pathways different from the old belief system. To make the shift more solid, research has shown it takes 21 - 30 days of practice; a mere fraction of the time it took you to acquire the initial negative pattern. What a relief!
I've been on both sides of the couples' equation -- married, single, dating, living together, and oh, single again. When I go out for drinks with girlfriends in long-term relationships, I'm shocked when they're jealous of my singleness.