Most of my friends are male. Platonic friends that I've had for 6-14 years. Handsome men but I'm not attracted to them and I certainly don't ever think "what if?"
And every interaction with these men can be accompanied by, or explained to, my SO with no difficulty. My male friends and I never cross the line in terms of where or how we hang out. It's never an intimate emotional or physical interaction. Never.
The man in this scenario chose to hang with a woman that he was not only attracted to but was
considering go further with. You can't have friends of the opposite sex if they are even a little more than platonic. If you have to wonder "do they like me" "would they cheat with me" "do they make me feel like I have to choose between them and my SO" "do they make me feel apologetic for having a SO and not spending time with them or wanting them" then these aren't platonic friendships and they need to be reduced in status to casual acquaintance or cancelled altogether.
Our daily interactions with people are only as complicated and dramatic as we make them. Stop signing up for complications and drama, folks.