Mark 10:11-12

11So Jesus said to them, ‘A man must not send his wife away and then marry another woman. If he does that, he has not been faithful to his wife. It is the same as if he had sex with another man's wife.

12In the same way, a woman must not leave her husband and then marry another man. She also has done a wrong thing. It is the same as if she had sex with another woman's husband.’