well, you have songs like Motley Crue's You're All I need...
Youre all I need, make you only mine
I love you so I set you free
I had to take your life
Youre all I need, youre all I need
And I loved you but you didnt love me

or how about G'N'R's Used to Love her?
I used to love her, but I had to kill her
I used to love her, but I had to kill her
I knew I miss her
So I had to keep her
She's buried right in my back yard