You aren't being fair to her or yourself if you date right now. You need to get to the point where you still think about the ex, but want to stop, that's a good time to start dating. You sound like you are still hypnotized. You are going to hurt this new girl if she really starts to like you. Getting someone new isn't always the way to forget the past. You aren't ready.
If you want to move on then yes but if you really want her back then you should try talking to her. Being sweet and romantic to a girl can help. She may have the same feelings. Take it from a girl who knows.
That, I'm guessing, Is called a rebound. The person you date or sleep with to get back on your feet after a nasty breakup. I wouldn't know much about that because I'm quite young. If you are doing it because you care about this other woman, then yes, you should, it gives you a chance to start something new and move forward. You won't be stuck on that same person forever. Good luck! :)