You cannot say " I have no heart to do sth." For example, Chicken soup for soul, not for hearts. . z- T: J$ O) ~. mYour context is not very clear. So can you explain the contexts more clearly? 6 s. f/ a" M: B- N3 dWhy you don't want to bother the boy again?
For the first context, just say I am sorry to bother you again. ! S9 S2 P# [2 o' _+ ?6 `- F
For the second case, I don't think you can use hearts in this expression. You can say I am not meant to do sth...
i am not comfortable to bother you again & K: W7 u- I. F+ U% n& h' b6 _0 T6 J8 c
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i am too shy to talk with the boy6 t0 @6 U; k! g4 E# s