Do you feel you're obligated to tell a sibling that their partner is cheating on them?

Do you feel youre obligated to tell a sibling that their partner is cheating on them?

A lot of people feel that if someone were cheating on their friend, it's none of their business to tell them either because they don't want to get involved or "be responsible" for potentially ruining their relationship especially if kids are involved. Does that apply to family or is family a different situation? If you caught your siblings partner cheating, would you immediately tell your sibling?

Do you feel you're obligated to tell a sibling that their partner is cheating on them?
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