Every girl i meet i compare to my ex

And no matter how good they are, they don't compare to her, well they prolly do, but not to me. My ex and I have been seperated since before summer. It was realy realy rough on me, but some how i got through it. I started to date, alot actually. And no matter how perfect the girl is, she isn't good enough
When does this stop? Ultimately, I'd just like my ex back, but I don't know how to do that. We are on good terms, she asks me to hang out, but I'm scared heh.