反脸无情

to turn one's face against sb and show no mercy (idiom); to turn against a friend

to fall out with sb and become hostile

to forget favors and violate justice (idiom); ingratitude to a friend; to kick a benefactor in the teeth

to fall out with sb; to become hostile

(idiom) to fall out with sb; to become enemies

completely lacking any feeling or sense of justice (idiom); cold and ruthless