I think of "cheating" as doing something your partner is not aware of or does not consent to.

I've "fucked" another man and my husband was aware of it, hell it was his idea...and I do not in the slightest feel I've "cheated" on my husband. even if I were to kiss another guy and my husband did not know what was going on, then I'd feel like I was cheating. And vice versa.

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XOXO