What can I do to stop thinking about her?

So in october my relationship of two years ended. I would love to say it was mutual, but in fact it was one sided. I'll give you three guesses on who decided to end the relationship. Its been over 7 months since I have talked to or heard from my ex. Yet I cant stop thinking about her. Its not like I actively think about her. The thoughts are more secondary. For example, I would order a pizza and I would think weather or not I should get green peppers because I know she doesn't like green peppers. I know that she is obviously not going to be eating the pizza. Why do I keep thinking like that? I have had my rebounds. There were the few rebounds just for sex, and then the one I genuinely liked for reasons other just sex. Yet even after doing all these things she is still the one I think about before I go to sleep.

I would just like to know what other people in my situation did to stop thinking about an ex. And is it normal to compare every girl I have met in the last year to this one person?