This kind of thing can happen in any group of people. Marriages do break down, people do find new partners, wives (and husbands) who've been freed from unhappy marriages do sometimes look great afterward.
Frankly, what bothers me is not what these couples are doing, but the attitudes of people like the previous posters. Frankly, it's none of your business. In the first case, here are three people, apparently trying to handle a difficult situation civilly and without disrupting their lives too much. If you really cared about them, you'd be supportive, not snarky. In the second case, please spare me your sympathy for the wife. If you were really sympathetic, you wouldn't talk behind their back and make jokes about it.
In reality, people do find the sexual and marital behavior of their acquaintances entertaining and gossip is fun. But at least admit that's what you're doing and spare everyone your fake moralizing.