I don't know where the mega-orgy idea comes from. Anthropologically, humans survived by being multi-maters. That doesn't imply it was mindless or without caring, or that it implies huge numbers of partners (rather than 2 or 3).

Pair bonding has always been a part of human societies. "Indeed, marriage as an elementary principle of human kinship systems has long been considered a central aspect of between-group alliances." But pair-bonding has only implied strict sexual monogamy relatively recently. Because humans survived by being multi-maters - and in some parts of the world that still takes place. There is absolutely no reason (except for modern Western beliefs) to think that implies that sex has no meaning or that there is no affection between those who choose to mate.

Humans are an incredibly social species. Amongst other primates, sex is often used to promote social bonding and connection. I don't understand why you think that implies mindlessness if humans were to do that as well? And that's aside from the fact that marriage for love is really only a couple hundred years old.

Even amongst swingers, there tends to be a lot of community and affection, and certainly amongst polyamorists there is. Hook-up culture is another thing, but I see no reason to overlay that dynamic atop the rest of human history and mating.