Don’t have the heart (to do something) 忍心(做某事)
e.g. She asked me to go with her and I didn’t have the heart to refuse. 她要我同她一起去,我不忍心拒绝她。
e.g. I didn't have the heart to tell her that I didn't love her anymore. 我不忍心告诉她我不爱她了。
e.g. I don’t have the heart to be a debt collector. 我不忍心做催收账款的人。