Ugh... I know you can't expect emotional reactions to be rational but jeez that's such a lame reason to swear off of love. He didn't have his heart broken or nothing, all that happened is that he once had a dumb friend who refused to listen. And from that he concluded it's best to stay forever...
So a lot of people are talking about what Himari and the other girls are doing, but isn't Saito to blame for a lot of this as well? He just goes along with whatever, getting into questionable situations with every girl for no reason when he's already married and clearly has feelings for Akane...
Yukino is holding a Ricoh Hi-Color 35S on the cover page, if we take it as canon that would place the manga around 1970 which I think is the first clear indication of when it's taking place. I would have guessed 1960s before this personally.