Everything is about give-and-take in this world.
To place oneself in a relationship = Double entry system
i.e.: As someone appears in your life, an account is opened both his and your life accounts book. Every event is recorded, consciously or otherwise.
Somehow something happened and you split up.
The account remains.
Balanced or not, if not, the position of balance b/d.
Debit - you earn something.
Credit - you lose something.
No matter which party had to bear the loss, or both parties earned something from the relationship. Both left something in common for each other - memories.
I guess everything applies from all the theories that we learn in school, what makes the difference is probably just the point of views.
Enough said. Account closed. =)