The moral of that story is: "The grass is always greener on the other side of the fence." I can't think of a more apt example than a married person feeling discontented with their own spouse as they lust for the spouse next-door.
It sounds dramatic and whirlwind-romantic, but I wonder about the prognosis for second marriages that begin in that way. You're talking about children who knew one another, probably played together, and knew (and trusted) the parents next-door. Now that parent is moving in and playing daddy? Doesn't bode well.
A friend of mine dated a dentist who had had a long-time practice with a close friend with whom he had gone to dental school. The two families knew each other well and lived in the same town. Needless to say, this successful dentist proceeded to fall in love with his partner's wife, causing both families as well as the practice to blow up. The lovers got married, and he moved into his wife's house with her children. Though the children lived with him for years, they never forgave him for ruining their lives. When his step-daughter eventually got married, he paid $30,000 toward her wedding, hoping for exoneration. Still she hated him. The upshot: husband and wife #2 got divorced. He explained to my friend that the children's resentment and misery ultimately drove him and his second wife apart, destroying the marriage.
So what did they leave in their wake? two broken families, two sets of unhappy kids, a second divorce, and a ruined practice and friendship for the former partners.