Forget about putting your foot down and all that nonsense because if you think she'll cheat she might just say f*ck it he doesn't trust me anyway might as well do it.
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Co-workers or not these are strangers, they are not in a big group but a small and intimate group, these guys have no obligation to you, for all you know this villa could be their "slaughtering" ground"
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But aside from the scare stories what it boils down to are your conflicting values (maybe these values reinforced themselves when you cheated because you know how easy it is)
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