To refuse to support someone and leave them without helping
به کسی پشت کردن
When she needed my help I turned my back on her and left her alone and now I feel very bad.
turn your back (on somebody/something)
a) to refuse to help, support, or be involved with someone or something :
How can you turn your back on your own mother?
In his twenties he turned his back on his Catholic faith.
b) to turn so that your back is pointing towards someone or something, and you are not looking at them :
Angrily, she turned her back on him.
turn your back on sb/sth
1 to move so that you are standing or sitting with your back facing sb/sth
When on stage, try not to turn your back on the audience.
2 to reject sb/sth that you have previously been connected with
She turned her back on them when they needed her.
Some newspapers have turned their backs on discussion and argument.
Oxford Advanced Learner’s Dictionary, 8th edition
Cambridge Advanced Learner's Dictionary - 4th Edition
turn your back on sb
C2 to refuse to help someone:
Surely you won't turn your back on them?
© Cambridge University Press 2013
phrase [VERB inflects, PHRASE noun]
If you turn your back on someone or something, you ignore them, leave them, or reject them.