Stuck-heart

A relationship or friendship ( good or bad ) that you can’t get out of your head, which you thought had faded long ago but is still somehow alive and you have the need and want to get rid of that feeling.

I really can’t get her out of my head. She is the stuck-heart in my mind.

You can’t actually use it in a sentence really it’s more of a word that is used in your head and as a way to reflect and understand a emotional feeling.