Tā yīnwèi luàngǎo nánnǚ guānxi bèi kāichú le dǎngjí.
He was expelled from the Party for sexual misconduct.
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乱搞男女关系 is the standard wording in Chinese disciplinary, legal, and news contexts for sexual misconduct or affairs - particularly in Party discipline reports. The English equivalent in formal CCP translations is often 'improper sexual relations.'
culture
During the Mao era this phrase carried serious political weight: being accused of 乱搞男女关系 (chaotically engaging in male-female relations) could derail a career. It still appears in modern anti-corruption findings against 落马 (fallen) officials.