First in danger, now trapped, best tap the title and see what comments might help you.

I'm trapped inside a curving cage

Contained, my music is assuaged,

I rap against the bars in beat.

I skip as come a soul so sweet

And gone and left me trapped inside this bond

And yet, for the soul I grow fond.

'So you met a soul but was left alone?'
'Yes, the soul came but is no longer in.'

Riddle Answer A Heart

Riddle Explanation
I'm trapped inside a curving cage - a rib cage.

contained, my music is assuaged, I rap against the bars in beat - a heart beat.

I skip as come a soul so sweet - the heart skips a beat.

and gone and left me trapped inside this bond and yet, for the soul I grow fond - absence makes the heart grow fonder.