Grudge

A deep-seated feeling of resentment.
Something that is held against someone for an issue they haven't discussed or resolved peacefully.

"I wish I could believe you then I'll be alright
But now everything you told me really don't apply to the way I feel inside
Loving you was easy once upon a time...

Just can't seem to get over the way you hurt me
Don't know how you gave another who didn't mean a thing the very thing you gave to me
I thought I could forgive you and I know you've changed
As much as I wanna trust you I know it ain't the same

I may never understand why
I'm doing the best that I can and I tried and I tried to forget this
But I'm much too full of resentment "

Beyonce - Resentment