Long-distance relationships require a lot of work and inner strength. If the loved one usually lives with you, and either one of you is working far away or abroad, the relationship can stay alive and faithful through daily contact by email, Skype or phone.
If the loved one's usual home is within the same country but far away, the relationship can stay alive, but even with daily contact, emotional and sexual faithfulness may be tested. For some people, especially marrieds, such faithfulness is non-negotiable. Others are sometimes willing to understand that a long-distance relationship has an element of risk.
If you normally live in different countries -- let's say you went abroad and met a charming person there -- the relationship is not likely to survive. The partners may have good intentions, but cultural and family issues will further stress the already fragile long-distance relationship.