Well learn from your mistakes and make sure not to repeat whatever it was that made things go stale when you get another girlfriend. You just have to view relationships gone stale like a wounded animal destined to die.. you know it's going to die, so you might as well put it out of it's misery before things start to become really tormenting and painful.
From what I know about things, I honestly think you made a good decision that was in the best interests for both of you.
I mean, if you had stayed with her longer.. it would have really hurt you more in the end, and there was no hope in getting her to have those feelings for you again so you should have no regrets, it happened and it was inevitable.