Opening Credits:
Smash Mouth - Walkin' on the Sun

Waking Up:
Bonoparti.lv - Questa Notte

Falling in Love:
Alphaville - Forever Young

Fight scene:
Keane - This is the Last Time

Breaking up:
The Killers - Andy, You're A Star

Getting back together:
Jesse McCartney - Kissing You Goodbye

Secret Love:
Bobby Vinton - Take Good Care of My Baby

Life's okay:
My Chemical Romance - Welcome to the Black Parade

Mental breakdown:
Jeff Buckley - Hallelujah

Driving:
Take That - Patience

Flashback:
Damien Rice - The Blowers Daughter

Partying:
Ray Charles - Hit the road Jack

Happy dance:
Golden Earring - Twilight Zone

Regretting:
Paul Anka - Save the Last Dance for Me

Long night alone:
Abba - Money, Money, Money

Death scene:
The Shirelles - Please Mr. Postman
(know why you haven't got a letter from your boyfriend? Because he's dead.)

Ending credits:
Abba - Take a chance on me

Well up until the party song it was mostly a slow and laid back film and then it went cheerier and faster. And it didn't mostly make sense at all.