Step one. Find and play with a puppy, dog, or kitten. Anything you can't possibly stay mad at for more than 10 seconds even if they ruin your shoes.
Yep, this part sucks. You can hear and even agree with all the logic in the world but this is an emotional reaction. You've heard it before. It will take time. It will be a sore point for a while, but each day you'll get on with things a bit more, enjoy things a bit more, think about him a bit less. This part is what all the friends getting you to do stuff is really good for. Go off and vent at the boxing club, shooting range, mountain top or whatever and then come back to them.
in the meantime *hug*
now go find that puppy