I'll give you the typical response guys give each other, find another girl and spend some time with her. It doesn't have to be serious, let her know that you're not looking for a steady relationship and someone to just have some fun with.

Your situation is really rough having to see her every day, I know if I had to see an ex every day after splitting up with her i wouldn't be able to handle it very well either.

Try to take pride in the fact that you weren't the one who did something low down and dirty, you didn't cheat, you kept your integrity, you're better than her.