Wiktionary
vb. 1 (context intransitive idiomatic English) To cease paying attention to something. 2 (context intransitive idiomatic with "on" English) To forsake, to abandon; to ignore.
Usage examples of "turn one's back".
To turn one's back on the King was to Hornblower a breach of good manners, something damaging, in some degree, to the conventions which held the country together in the face of its imminent peril.
And it's a hard thing to pass everything by all one's life, to turn one's back upon everything, to forget one's mother and decorously accept the insults inflicted on one's sister.
The point was not to turn one's back on technology, as Larry Smith's Cheyenne were attempting to do, but to subordinate it to the living souls of men and women.
One does not follow a pair of lovers to that extent, and one is accustomed to turn one's back on the drama as soon as it puts a wedding nosegay in its buttonhole.