The Lure of Forbidden Love

Forbidden love.  Could there possibly be a scenario more seductive than a relationship that can't/shouldn't be?  And if there is an element of tragedy, the level of temptation only increases tenfold.  For example, in the paranormal genre; the relationship between mortal and vampire is forbidden because of the vampire's lust for blood and the obvious danger it poses for the fragile human.  Vampire's are also reported to be immortal and incapable of aging beyond the day they were transformed into bloodsucking creatures of the night.  So, the idea of hooking up with someone who will never look into a mirror and anguish over a sagging butt or turkey neck might not be tenable for the long term.  But again-so enticing to live only for the immediate moment with no thought of tomorrow.....