The best way to forget your previous relationship is by resolving the issues that bother you about the relationship. You should try to overcome the negative after effects of the relationship that has got over and cope up with the loss. This will help you to be a positive person and cope with the situation.

It is not about FORGETTING past relationships. It is about HEALING - the emotional and mental pain associated with them.  If you do not heal the past relationship - it will continue to torment you. Understanding (what & why things happened, etc.), acceptance and forgiveness (of your own self and others) is the key. Speak to a counsellor and get help in healing - it will help you effectively close the past and move forward in peace and harmony. 

Greetings! The replies by my colleagues have nicely clarified the situation for you and hope you are following those. Nice keep it up! In addition, I am proposing an assignment for you. Make out a list of the actual scenarios, activities with respect to your social set up, which you envisage and want to keep up in future. This may have to be written a number of times, incorporating changes and rewriting. After you finish, the understanding will be clear. At that time you can have a discussion with your psychologist and get more guidance. Best wishes!