不忍心
「不忍心告訴某人」是not have the heart to tell sb
I didn't have the heart to tell her that her beautiful vase was broken. (Longman Dictionary)
We knew all along but didn't have the heart to tell her.(COBUILD Dictionary)
The Chinese Government is increasingly dissatisfied with Mr Tung for his apparent lack of wisdom but doesn't have the heart to tell him.（阿東）阿東洩露了國家機密！