Ladies. Help 😞

So...my boyfriend and I were talking yesterday and he tells me about a comment his mom made that he completely disagreed with. Basically, if a partner is cheating in a relationship, then that partner shouldn’t say anything/keep it a secret for the sake of the relationship. He completely disagrees but....doesn’t the Apple not fall from the Apple tree? I’m pretty emotionally disturbed that his mom would think that way, and give advice like that to her son