I need to stop thinking about an ex, any idea's?

For those of you who have been following this whole mess with my now ex girlfriend then I you can skip below and go right to the actual question.

So I recently went through some really difficult situations with my girlfriend at the time. Needless to say it didn’t end well and she cheated on me with some guy while she was on vacation.

Anyways I’ve broken up with her but the problem is I can’t seem to stop thinking about her. I have no intention of getting back together with her but I find myself horrified that I may never get to speak to her again.

I guess what I’m wondering is if anyone can suggest good ways of keeping your mind off someone? Any idea’s would be very very much appreciated.