It can’t be me, you’re saying goodbye to
It can’t be me, you’re letting go
It can’t be me, which feels all this pain
It can’t be me, the last to know
It can’t be me, to keep you company
It can’t be me, to help you now
It can’t be me, to mend your heart
It can’t be me, to save you somehow
It can’t be me, sitting in the dark
It can’t be me, crying all these tears
It can’t be me, that’s being ignored
It can’t be me, wanting back those precious years
It can’t be me, the savior of your sanity
It can’t be me, the keeper of your happiness
It can’t be me, to keep you from falling
It can’t be me, right now I need you less
It can’t be me, that’s what I was told
So I sit and contemplate what’s to become of me
When she was all I wanted to love and hold.
I like the phrase "savior of your sanity," so much in fact, that I might borrow it.
Otherwise, I think the repetition of the backbone phrase and title works well, and the fact that you only use it once in the last stanza is a nice because it's a break in the rhyme scheme and repetition. The uniqueness of it in comparison to the previous stanza ties it up nicely in a little bow, so to speak.
Reminds me of Shakespearean sonnets, where the last stanza is set apart from the others.