To my knowledge, "marriage" has meant "a man + a woman for a lifetime" in most societies that I am aware of. (In the context of this conversation, I think the lifetime part is what the parent was talking about.) Frequently a man could have multiple marriages, but each was for a lifetime. It might be acceptable to have a mistresses outside the marriage (Rome), but the heirs came from the official wife. I'm told that the pre-Christian Irish renewed (or didn't) their marriages every year. Divorce also existed; I know that both the Romans and the Mosaic Law had divorces. But marriage was usually taken pretty seriously by all societies, especially agricultural ones, regardless of whether they were Christian. The idea that "it's just a piece of paper" seems to me to be fairly rare. Maybe the Romans had that (I think Cicero divorces his old wife for a new young one when he was old), and Jesus criticizes the Pharisees for no-fault divorces, but these seem unusual situations compared to most of history.