Find a way to make peace with your trust issues. It's cool if you don't want your ex anymore. I too decided long ago that stressing out over the specific girl I liked wasn't worth it, that I'd get on with life and trust God to send great matches my way, be it that specific girl or someone else. And I met some new girls who were awesome, definitely more of what I wanted in my life. But the same insecurities I had before kept popping up and messing me up because I was unwilling to deal with them. That's why I think it's good to take a look at the negative patterns in your old relationships, take a look at the areas of resistance you have about yourself and your relationship to love and see if you can change that. As for the new girl, I'd just ask her out and talk to her more, see how it goes - but that's me, you probably already know what to do.