It strongly depends on what kind of relations you are talking about.

I'm strongly convinced that if the couple doesn't have the possibility to be together, earlier or later they will split up. Otherwise, they will decide that living like that, separatedly, is a torture, and they will become happy changing their life and living together. :) I've never seen the least variant, unfortunately... But I believe it is possible. Very good question! :)

For short time is ok,but seems hard if a couple could not see each other that often,personally.

To attain it, the two persons should really be in love with each other and that they put God at the center of their relationship and make sure that they love continue to flourish even though they are apart. Moreover, there should be the big letter " F"-and that is Faithfulness.

Maybe yes. Relationship can last long if both of them want to maintain it or they have something in common such as same purpose, same interest.