@Spaz tried practicing mindfulness?
It's something I try to implement in my daily life yeah.
Yep... this works for me.... Take some yoga practices, believe it or not that really does help. Not only will it help you getting re-centered you'll get in shape, and get to practice around hot chicks.... I met lots of chicks in yoga. I pay $120 a month for unlimited access to practice and a studio, which is a lot cheaper than therapy and you get better results. But stick with it, it's hard at first and like everything it gets easier and more effective with time.
There is always room for self-improvement, take the time and focus on that. But understand, it really isn't about you, it was that this new dude had something you didn't, that right now, she FEELS she needs... it could have been ANYTHING, that does not make him better or worst. Somewhere down the line your ex-chick's emotional winds will change again, and new dude will be left wondering W-T-F happened, either that or he will lock her down and then she will drive him crazy trying to keep her... just think about that.
But for you the ride is over... just go find another better ride... best medicine for this sort of thing.