Long distance relationships are very difficult. Mine recently ended after a year and a half of happiness. In a span of two weeks it went from "We're gonna live happily after!" into "Hi! I haven't heard from you in a while, I miss you! ...Um, have you been ignoring me lately? Can we talk this over and work this out?" "It's over, I don't love you anymore." "Oh, okay. "
Long distance only works if both parties try to make it work, just like any normal relationship. If one side becomes distant they're not going to magically embrace the other side and say "We'll get through this!" They're most likely going to break the other persons heart into pieces, leaving the other person wondering what the hell just happened.
But if both sides are pretty loyal and don't mind the loneliness, there's a chance they could work.
It's not like a friendship where you can ignore your friends for a while and then catch up with them later, or moving across the country away from family. You'll always be family to them. But in a relationship, if one side is tired of being too far away they'll say goodbye, and you should always be prepared for that even if you think "It won't happen to us! We're invincible!"