Time - it's easily the most powerful tool in your toolset. You can just sit back and wait like a year or two. Then you're magically either over it or semi over-it and ready for other tools to work.

Also: dating somebody else. Just be clear up front you're getting over a breakup (i.e. you're not good relationship material right now).

Runners up: working on yourself: working out, eating right, learning new skills, leveling up at work, etc