Personally, I'm repulsed by talk about a dual family system, one for adult love and one for kids, though there's no reason on Earth somebody couldn't do that now. Of course, virtually nobody does because it's a hornet's nest of emotional trouble, and because people's rising expectation (having happiness at both levels) is a very good thing, even if often not done well. Imagine the split system: "Goodnight, Jenny and Johnny! I'm off to my adult lover now! Don't worry about mommy. She's not really that sad. She'll cry herself to sleep."