This is true, what he has done is extremely predictable/cliche, disrespectful and quite cruel even without the cheating .
Also wanted to say pp making digs at the friend are wrong. He is a single man with no kids and is espousing the philosophy which suits his lifestyle. He or anyone else who is single and child free is not “selfish” he just doesn’t have to consider his (non-existent) wife and kids and that’s ok
He didn’t force OPs husband to bluntly apply his “new way of thinking” to his life. He merely announced it to Op partners who decided to replicate it. But he must have had an appetite for it anyway to so readily decide to follow suit.
It’s just common sense and decency for OPs partner to know he can’t live the exact same way as his single with no kids friend.
Me and a few friends met up a while back in our early 30s, some had kids some didn’t, out of the ones who didn’t have kids one was talking about how important it was for her to get up and do last minute things ( local trips, trips abroad etc ). another friend at the brunch who had been married with kids since her early 20s was thoughtfully reflecting aloud on how she could incorporate some of that into her own life given that she was married with 3 kids and worked full time. I don’t know if it was a result of that conversation but since then she has been on quite a few solo and/or childfree trips but she discusses it with her partner, reciprocates so he gets his time away too and also makes sure it’s not causing the burden to shift to him.
It was 100% his responsibility to figure out with his wife if/how he could apply that way of living to his life, while taking into consideration his whole family.