There are many times where you have to stop dwelling over the past and start moving on. Going back to the old memories will only hurt you and this way you won't be able to forget him/her. Try not to think about your past and erase both the good as well as the bad memories.

Give yourself some time to grieve
Even though you must not dwell on the past; the best thing you can do is to give yourself some time to feel bad about it so that it helps you move over fast. As strange as it may sound, grieving over something helps you to not think about it again. Thus make sure that you lend yourself ample time to feel bad about the situation.

Remember that you will love again
Just remember that love has not gone out of your life completely. Thus don't brood over what's gone wrong for a very long time. Give yourself another chance and start mingling and socialising again. You might find someone better this time.