Are you sitting at home crying your heart out while your ex is out there having the time of his/her life?  By now you should have realized that it is no use crying bitter tears.
While it is understandable that you are devastated on account of being betrayed, it is stupid to allow yourself to go to pieces! Regretting the past will not change it - doing something positive towards getting your life back, is! Be active and not passive.
Don't sit back hoping and wishing your ex is going to call.
Get a hold of yourself and build up your confidence and ego.
Tell yourself that you are worth loving! It is possible that you have neglected your looks for too long! Well, it is never too late to change that.
The more beautiful and attractive you look - the more confident you will feel! Be cheerful and happy.
You will have to work on this, but the faster you get that smile back on your face the better it is for you! Join a club, gym and make new friends.
Your ex should see the effort you are making and be pleasantly surprised to see you becoming popular and happy.
Chuck the bad habits.
Bad habits and attitudes have a nasty way of pulling you down.
Get rid of them pronto! Portray a loving and caring nature to one and all.
Your ex will be the first to notice this change in you.
  Keep mutual friends so that you will always have an opportunity to meet up with your ex without it being too noticeable! There is no way your ex is not going to ogle the new body, attitude and confidence.
Show that you still care! It is more than possible that your ex still carries a torch for you no matter what his/her behavior towards you has been.
Subtle flirting and intimate smiles reserved just for your ex should rope him/her in!