People in a committed relationship generally make plans for their future as a couple. They do not usually see themselves apart, but this does happen in the modern world. Work is often the culprit when this occurs. A couple will get along famously, but then one is offered a great job in a distant land. The couple knows this will be good for their future. They decide together that one person will travel, and the other person will keep their job at home.
Being physically separated does have consequences for some couples, and modern communication cannot always make up for the distance they must endure. The perceptions of both people change as they now face a life without their partner. They might take up new hobbies, meet new people and see other possible relationships. While sad, the partner that discovers someone else has outgrown their existing relationship, and they must end it before hurting their significant other too much.