Time. It's cliche as hell but time heals all wounds. Sadly there will be someone that slipped away that you will think of years later, the pain won't be there, but you will think of them randomly.
Also if you realize you're slipping i to depression seek help from a professional. Depression will beat even the strongest person down. Talking to someone will help.
Try and connect with anyone else but her. Family, friends, strangers, whoever. I got over my breakup by transforming the way I interacted with people around me.