Unrequited love (to me):
Imagine being underwater; short of breath. You can see the surface; so tantalisingly close you feel you need only reach out your hand and then suddenly so very far away, beyond your grasp. So perfect, so beautiful and irresistible. Yet, deep down you know it's an illusion and when you surface, as you must, it will be broken but you will survive. Yet you choose to remain below and slowly drown.
Damn, I gotta break this run of good moods....