I find a distraction. A movie, baking something, just anything to keep me from thinking
try to get in touch with the person even if it means to get hurt
Do something, if you have a hobby do that. It is good to find ways to be happily engaged when you are away from someone you care about, it helps you to become a more complete person. Otherwise their is a danger of becoming needy or clingy etc.. Try to be self satisfied.
I write emails to him.