Friends and and their marriages

Over the last couple of weeks, I have been informed by friends who were having some sort of problems in their marriage lives. Strange enough, all of them were the husbands. There was this friend from long, long ago, who had divorced the same wife for the second time and was contemplating reconcilliation but stopped halfway because he was not totally sure that he wanted to go down the road again with the same ex-wife. And along the way, came a long-lost lover, whom has also recently got divorced with 3 kids, and he was seriously considering a marriage with this woman albeit the 'package'

Another friend, whom I see as happily married with a kid, was recently being hunted by a long-lost, still single, lover. I didn't really understand the equation here. What's the ex-lover's motive? Why did this friend obliged to the conquest? What would happen if the wife knows of the situation? (By the way, I am acquainted with his wife)

The third friend, who ditched a woman he said he loved and married another, with whom he got a few kids, came back to hunt the ditched woman (whom by now had already married another guy), requesting her to become his secret lover. Complicated? You bet! Understanding the situation had already make my head went spinning...hehe..

I've heard of middle age crisis. But my friend are all in their 30s. What causes all these complications? Is there really a quarter life crisis as well?

For now, I can only be their ears. Offered some of my thoughts, but not going to do more than that. Will just look and see what will happen and hope for the best for all of them.