Both social norms and laws are the result of a balance between personal freedom and the necessary restrictions imposed on those freedoms to ensure that the social order is maintained.
Or in other words, norms and laws represent some kind of balance within a social group between the desires of each individual, against their most obvious problematic outcomes for society at large.
In a social context where people can have wildly different desires, the satisfaction of which can have good and bad outcomes for other individuals, some limitations must be put in place, or the society will destroy itself. This is not the way the Buddha’s teachings arose.
The Buddha taught how to end personal suffering by learning how to end the craving and attachment for things that we cannot obtain, do not have, or should not desire, each of which cause us to suffer.
Thus, the goal of the Buddha was focused on helping each individual to have a better life, but in a way that also ensured harmony between people, because individuals in conflict suffer as a direct result of conflict. And if a society was based on these same principals, then there would probably not be a difference between how individuals comport themselves, and how society needs them to comport themselves.
But, most people, even some Buddhists, are ignorant of, or fail to properly apply the Buddha’s teaching to their own lives, so a society that truly implements the Buddha’s teaching is presently one of those things that a desire for will cause us to suffer, because our desire will be frustrated.
So no, you truly can’t rely on social norms and laws to be a guideline for what proper sexual conduct is from a Buddhist perspective. But you can be assured that sexual conduct that conforms to Buddha’s teaching will not violate social norms or laws.