comparing the person you are interested in, dating, wanting to talk to you from your first love?

I have a habit of comparing my first love (who cheated, lied,etc) to my guy friend that i have now. It seems like no matter how good the guy is. I always feel that that guy will do me the same way. I was soooo devastated when i broke up with my ex. The thing is that the relationship has been over for years now. Every guy that enters my life, i am very skeptical of that it is hard to give a guy a chance. It like i already have this mind set that they going to cheat, lie, etc. At the end, i will be hurt. I am tried of comparing because when i do this, i do not even want to try to put effort in the relationship.

How do I stop this? It is soo hard..