Is it cheating if your spouse knows?

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My aunt and her husband had a very open marriage. Toward the end of it, they both had affairs, but with each others' permission. They would even share the details with each other and actually became friends with each others' lovers. Now she's in a relationship with a guy and she's afraid to tell him about how her marriage went down hill and how they tried to fix things and ultimately divorced. So how does she tell her new boyfriend about her past experiences without it seeming like "cheating"? Is it cheating?