Friend cheating on their SO

Have you ever been in a situation where your friend is cheating on there SO and you want them to know they are being cheated on but shouldn’t say anything because of loyalty to your friend. I’ve in this situation with 2 different people one is my friend and she is cheating on her partner I want him to know because he doesn’t deserve that. The other situation is my husband friend cheated on his wife once and even had the nerve to use us as a excuse saying he was with us. He was actually at a coworkers house cheating on his wife with her. My husband thinks it’s wrong to but says it’s none of our business.

Would you keep to yourself because it’s none of your business and all you will be doing is putting yourself in other peoples drama. Or tell them because they deserve to know. Honestly what would you do?