I'll read this through bit by bit.

The first stanza shouts out defiance -"you can keep them to yourself "- and a new found confidence maybe? - "I no longer yearn for your approval or affection"

This draws me in as reader, as I want to see who this person you have obviously cared about but whose attention is no longer relevant, is.

The second stanza reveals that perhaps this person didn't themselves hurt you, but wouldn't listen to you when telling them who did......."a piece of you to believe my story....." so this person hurt you in a different - and perhaps more profound - way? "You just shut your eyes to my world and pretended you were blind". A sad truth, people don't want to face up to the truth.

Back, now, to a sign of greater confidence and certainly anger in the third stanza as the victim stands up to the one who should have stood up for her. But it's easy to be there for someone who doesn't need your help anymore, isn't it? "rehearsed excuses that are way too late" - this line tells me the sufferer feels the same!

Stanza four: The victim was shown no sympathy, so why should this person be shown any in their guilt? And none will be given, it seems. "I have no interest in easing the burden of your guilt."
No pleasure seems at this point to be taken by the victim in this person's guilt - just a continued anger: ....."which is eating through you years too late!" exclamation mark is highly effective here.

And then the final two lines, reinforcing the above - there is no time to be given to someone who had no time for you when it was needed the most.

A sad and powerful write, Saffie, that oozes anger and frustration.
Take care,
Ben