Unreturned love, for those of you with a less poetic nature!
Person 2: You've shat plastic bricks? You sick bastard!
A relationship is often built up in ones head, only to find out that the other person does not feel the same way, therefore it is unrequited.
A person who you cant seem to get out of your head, but they prefare to spend there time talking about some twat who treats them like shit!