not have the heart to do something
From Longman Dictionary of Contemporary Englishnot have the heart to do somethingnot have the heart to do somethingCAN'Tto be unable to do something because it will make someone unhappy I didn’t have the heart to tell her that her beautiful vase was broken. → heartExamples from the Corpusnot have the heart to do something• I didn't have the heart to tell my daughter we couldn't keep the puppy.