I ended a 6 year relationship...and I agonized over it for a year before hand. I'll tell you, I never slept so well as I did the night after I ended it. Once you know its over, its over. After I moved my shit out, into my own place, I sat down and smiled. It's not taking joy in hurting another person, its joy in helping yourself.
I was always looking at others, and imagining what it would be like to be with them and so on. In my current relationship, I will be honest, I do notice other women, but I don't start picturing in my head what life would be like there, because I'm where I need to be at home. You walk past and think, "yeah, she's pretty" and move on.
When you find the one, you'll know