Your best friend has told you she’s having an affair. Should you tell her husband?

The people caught in the crossfire of an affair aren’t always the partners being cheated on. Sometimes it’s the friends or colleagues made aware of an infidelity and left in an incredibly difficult position as a result. Do you turn a blind eye and become vaguely complicit? Or do you blow the whistle and betray a friend? Ellie Muir speaks to people who’ve been on both sides of the drama