Let go. Once you can accept this for what it is, surrender to what happened, than you can move on with calmness and peace.
Allow yourself time to greive but do not forget yourself. Take care of YOU. This means, pampering yourself. Doing things you enjoy.
Talk to people who can relate and understand. Peoplewho make you feel good about yourself should be welcomed, others who critisize and judge you should be left at a distance.
Do not call or text or e-mail them. The more they reject you, the worse off you will feel. Remember, you can not make someone want you or care.
Do not start looking at old pictures of you and this person.
Go out with freinds. People who you can relate too, people who make you laugh and feel good about yourself.
Listen to joyful upbeat music.
Do something you never did while in the relationship. In life when you look back, you will for the most part regret what you did not do in life, not what you did. So begin a journey and start living.
Try not to torture yourself with questions of why or how.