A class act to the end.
Two songs: The Carpenters’ “Intermission” followed by Meat Loaf’s “Two Out of Three Ain’t Bad”
I’m Over You* - Hootie & The Blowfish.
Don’t Come Around Here No More - Tom Petty & The Heartbreakers.
*and pretty much every other song by the same title.
Positively 4th Street, Dylan.
It Ain’t Me, Babe - Bob Dylan
(trend here?)
The entire Darkthrone album F.O.A.D.
Release Me - Engelbert Humperdinck
I know this is from a female p.o.v., but the feeling is universal:
Smile by Lily Allen 
Jesus, is the guy dumping you?
Well depending on her name and where she lives, how 'bout Maggie’s Farm? 
Love Stinks - J. Geils Band
Phil Collins - “You Know What I Mean”
Richard Thompson - “A Man In Need”
“Go Away” – Gloria Estefan
“Salt in My Tears” – Martin Briley
“You Keep Me Hanging On” – Kim Wilde
I just find this really mean–if he truly intends to send it. That said, I like Johnny Cash’s version of “It Ain’t Me, Babe”.
I’m going with the assumption that Saint Cad is either (A) kidding about sending it, or (B) has tried every other reasonable method of explaining the situation & the lady just doesn’t want to believe it. But I admit I’m making assumptions. I’d love to know the facts, but as I’m brand-new here I don’t expect Saint Cad to explain the details just because I ask.
You did see in the OP where he said that he needed this mix CD about fourteen years ago?
Why go with subtle:
I Hold Your Hand in Mine, Dear, Tom Lehrer
I’m with eleanorigby. If you ever did like or respect the person, why taint the last memory they have of you?
That said, if you want to put the cherry on the carelessly hurtful sundae, go for Zappa.
From Frank Zappa’s Go Cry on Somebody Else’s Shoulder:
A year ago today
Was when you went away
But now you come back knockin’ on my door
And you say you’re back to stay,
But I say…
Go cry
On somebody else’s shoulder
I’m somewhat wiser now
And one whole year older
I sure don’t need you now
And I don’t love you
Anymore
Wow, I really hope you never actually do this. Try telling the girl that you’re shipping out in the morning instead.
ETA: yeah, I read the OP and now that he needed it 14 years ago. Also, you might try “Because of You” by Kelly Clarkson. Some people think it’s romantic.
“Most Likely You Go Your Way And I’ll Go Mine” - Bob Dylan
“It’s All Over Now, Baby Blue” - Bob Dylan
And for the non-Dylanists:
“Feel A Whole Lot Better” - The Byrds
(“And I’ll probably feel a whole lot better when you’re gone”)
“It’s All Over Now” - Bobby Womack/The Rolling Stones
“I Don’t Love You” - Teddy Pendergrass
Two songs by Placebo:
Bulletproof Cupid– Although it seems as if it’s an instrumental and there are no truly discernible lyrics, it does have secret lyrics.