I don't adhere to it, but I'm not judging or downvoting you and don't know why others are. I'm surprised other commenters are surprised to be honest.
Surely I'm not the only one who has been subjected to a seemingly endless stream of rom-coms where the protag ditches their SO for their good/best/work friend my entire life? So it shouldn't be surprising that some people are wary after being subjected to such propaganda.
It can be an issue when one person in the relationship has way more opposite sex friends than the other. It's hard for some to admit their insecurities in that situation, so they silently accept it instead of having a fight over it (which probably would have been healthier).