I hate hate hate it when a friend group hides infidelity/ cheating from the victim (usually a friend in that group).
"No, I don't want to hurt their feelings, they eventually get to know. I'm not the one to interfere in their personal life. Maybe it's more to it than meets the eyes. Bla bla bla bla"
It's always a pain to get betrayed by your partner but also your friends??
You're supposed to inform your lovely friend about their cheating spouse/partner. No amount of excuses make up for this shit.
"Oh, but it causes drama, I don't want to interfere with it. I'll get dragged to it in their fight!"
Listen, if you get to know about their betrayal, it's 100% guaranteed that IT'LL BE DRAMA! There are two options: Tell them and be an honest friend or be a piece of shit/coward and be the second betrayer to them.
I'm just rephrasing what you're actually saying:
"I'm too cowardly of a person that I'll hurt my friend in the long run than to admit that I've been hiding their partner's betrayal. I'll continue to mask it as long as I don't get dragged into it."