A happy couple does not get disturbed even if somebody else takes interest of one of them. A relationship can seem happy, but there's nobody who can say that this is the best you can get. See people always want more than what they have. Don't take the talk seriously, there is no buddha among us. We're all selfish. That's why you want everybody else to live by their morals, because it would make you feel better. Isn't it selfish to demand somebody to live the way you feel is right?