If you're asking me whether or not you should date someone new, it depends on what kind of feelings you still have for your ex.
Getting over someone after a breakup takes time. The heart isn't a light switch: you can't just shut it off when a relationship ends. It's perfectly normal to have residual feelings for someone you have loved and with whom you have shared your life for months or years. The feelings will lessen with time, and I see no reason to lock yourself away in a vault until you are completely over the guy. Dating new people will do you good, though I do think you should be honest and let any new guy know that you are still getting over your last relationship. You don't have to elaborate; he doesn't need to know the particulars.
But, if you think you're still in love with your ex and can't stop thinking about him night and day, that's more than normal residual feelings. You will always love him in some sense, sure, but if you're obsessing about him or hoping to get back together, I don't think it's fair to start anything up with a new guy. Was the breakup mutual? Did you want it? Or did he dump you and you just haven't accepted it yet?
That's the big question here, whether or not you have come to terms with the split. You know in your heart whether you have or have not. If you're still thinking about ways to get back together with your ex, then you have no business dating anyone new yet. You don't want to hurt a guy by getting him interested in you, then dumping him the second your ex wants you back. If you're just missing what used to be, then get back on the horse and have some fun. The best way to get over someone is to meet somebody new.
Thanks for the question.
Like Cary said, If you are on any level still considering getting back together with the ex, then don't get involved with this new guy. It wouldn't be fair to either of you since there is no way that you'd be 100% involved in the relationship.
I mean just think about it in reverse, if you were in his shoes, would you want to start dating someone who could drop you at the drop of a hat to get back together with his ex, and that wouldn't every truly be present in the relationship because they're still hung up on the ex? Imagine how frustrating it'd be to get mixed messages and the weird push-pull type relationship that ensues from that (yes, I'm talking from experience).
Ugh, I need to send this link to my friend. She started dating tis guy who posts all over Facebook how in love with his ex he is and how much he wants her back. We all want to pull her aside and ask her if she thinks those statuses are about her, or how she justifies being with the guy. Ugh.
You have GOT to watch this video. And if it wont post, look up Taylor Mali "What teachers make" on youtube. it's great.
http://www.youtube.com/watch?v=RxsOVK4syxU