His marriage broke up over wife swapping because his wife fell in love with one of the other guys who was just a sweeter guy.
Sorry, nope. His marriage broke up for reasons that may have involved the other guy but their relationship was thiers to screw up. Her love for another guy would not automatically erase her love for her husband. That being said adding people to a relationship makes things more complicated, harder to balance, easier to take offense and to let fear and insecurity win. But I don't think you should blame her falling for the other guy, that implies that people can only really love one person at a time. I don't suffer from that handicap and believe that most are capable of loving most whom they know that are decent and good.
My wife cares very deeply for one of our friends in particular, a guy, (I love the guy too, just more platonically, lol) and shares my deep affection for another, a woman. Love is not an all or nothing thing and is not the reason people fall out of it with one another. Marriage is an arrangment seperate from love and although it is much better with it, many have survived without it. Ours even did for quite some time when I was inactive for 10 years and my wife was very devout.
The 'reality' is that life is complicated. Half of all marriages end in divorce. And I can masterbate quite effectivley without spending a thousand or more dollers on a doll thank you. ;)