Think of David Lynch's MULHOLLAND DRIVE, with it's dreamy narrative about (I believe) spurned love driven to violence. Has any film tapped into the strange logic of dreams like this one?

Or John Malkovitch's THE DANCER UPSTAIRS, where an idealistic man makes gestures of unrequited love towards a woman who cannot return them, both because of what she believes and represents, and because of what he represents and must protect.

Tom Tykwer's HEAVEN offers an interesting variation on the theme of unrequited love. You'd think Giovanni Ribisi's character would never win the heart of this unusual lady, but he does... his desperate acts to prove his love for her lead to an unlikely union in life and death.

Wong Kar Wai's IN THE MOOD FOR LOVE (and its sister film, 2046) also speaks eloquently about unrequited love, and a different kind of dream. Here the dream is the reliving of old events... putting moments where nothing happened on a pedestal because you were too scared to do anything about it at the time.

Michel Gondry's THE SCIENCE OF SLEEP is far from a great film.... bit of an indulgent mess actually. A shame - as it embodies both themes perfectly!

Perhaps we could even count Spielberg's AI here - David's dream of Oedipal bliss with Monica is unrequited throughout history, a tragedy of technology (that simulated love could cause an inhuman being to suffer pain they should never have borne).

JACOB'S LADDER - another great dream film.
FEMME FATALE - imperfect, but quite entertaining dream film...
PUNCHDRUNK LOVE - captures awkward romance to perfection. (As does ETERNAL SUNSHINE...) Neither involve unrequited love, but the romance feels too good to not mention here.