Y'know, the best advice has already been given: Live your life, go hit the town, mix things up, enjoy yourself....you will eventually think about him less, and feel better. It does take some time, and it is normal to mourn and go through all sorts of feelings.
When I was in a situation similiar to yours, I found myself thinking of ways to seek revenge. Not very mature, of course, but my thinking was " I have poured so much into this, and now I am being humiliated?! No way!".
A good friend of mine was clever enough to show me a way to harness that powerful energy without destroying myself.
Here's what she said " For every moment you dwell on him, he wins. For every moment you give to yourself, you win. "
I got real into "winning" and getting 'one up' on him.
Eventually I looked around and my life was improving, and he wasn't in it.
I started enjoying myself. I no longer cared about what he was doing at all.
In fact, the happier I became, the more genuinely I wished him well....
in a life without me!
I learnt that love doesn't =investment. Nope, it isn't like putting money in a savings account. hahaa. It was a seriously rough lesson.
The ol' "The best revenge is living well" thing.
Hey, it really is true.
Look at how his happiness is driving you nuts.
You don't deserve to suffer over it anymore.
Go ahead and let it go.
You deserve to think about whatever you want.
Do you really want to focus on him?
Look at how much you are learning from having had that relationship.
Look at how much you can do now that it is over.
Take care.
Have fun exploring jen again.