How do you deal with being far away from people you care about?

This situation can arise in many different forms. Your best friend moves somewhere for a job, SO moves away to college, or you make a friend online. How do you deal with not being able to do the things that you normally would? It’s excruciatingly difficult for me to see someone who is sad and not be able to do anything about it. It’s equally difficult to not be able to celebrate good things along with that person. What do you do to combat these feelings?