Is an open marriage the most idiotic thing ever?

I'm friends with a couple in their mid 40's that just moved in several months ago. Their two children are already in their 20's living on other states. The woman admitted that they've been in an open marriage for the longest. They have a rule about informing who they're hanging out with, no feelings between the other person and if the person will be at home.

Needless to say, this is a ''what the hell did I just heard'' moment for me. Isn't this the most idiotic thing ever? Open marriage... who does that?

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3 mo
Both claimed to love each other greatly and that sex is different than love.
Is an open marriage the most idiotic thing ever?
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