3 sentences

1. 他背着妻子在外面和人勾搭。

   tā bèi zhe qī​zi zài wài​miàn hé rén gōu​da.

   He was cheating on his wife and carrying on with someone else.

   Source: Dong Chinese Dictionary

2. 他们二人私通，勾搭成奸，被众人撞见了。

   tā​men èr rén sī​tōng, gōu​da chéng jiān, bèi zhòng​rén zhuàng​jiàn le.

   The two of them had an affair and were caught in the act of adultery.

   Source: Dong Chinese Dictionary

3. 他们勾搭在一起，干了不少违法的勾当。

   tā​men gōu​da zài yī​qǐ, gàn le bù​shǎo wéi​fǎ de gòu​dàng.

   They teamed up and committed many illegal acts.

   Source: Dong Chinese Dictionary