Corundum Crucible

I'm not sorry, but 
Please accept my apology 

I don't wish I could take it back, but 
I hope I learned never to do it again 

To say this has been a hard lesson 
Is the understatement of the century 

Rather, call it my corundum crucible 
'cause this conundrum has tempered me 

Though it has hardened my mind 
It has softened my heart, finally 

Tenderness, a frightening vulnerability 
Also the only way I can really feel Ü 

So that if I ever get another chance #2 
Know the heart on my sleeve is Proof