harden your heart against somebody/something
harden (one's) heart against (someone or something)
1. To stop feeling kindness and compassion toward someone or something. Don't harden your heart against people who need our help. It's not their fault they're in that situation.
2. To cause one to stop feeling kindness and compassion toward someone or something. I worry that all the trauma she's already been through at such a young age will harden her heart against other people.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
ˌharden your ˈheart against somebody/somethingno longer be emotionally affected by somebody/something because you feel angry, bitter, etc., towards them/it: Doctors have to harden their hearts against the suffering they see every day.
Farlex Partner Idioms Dictionary © Farlex 2017