Dating in the workplace is usually a bad idea, especially if it's a manager and an underling because the power dynamics get fucked up.

But in the case of the Clinton affair, it was effectively personal (Bill, Monica, Hillary) -- their business.

Please explain how this impacted Clinton's ability to execute his job, or how that dynamic hurt Lewinsky in such a way that it needed to be a national affair?

This is the same kind of feigned moral panic over Hunter Biden's business dealings -- designed solely to smear the president for their opponents political gain.

Edit: as a counter point, Trump fucking a porn star months after his son was born was technically between him, Stormy, and Melania. The reason that it was worthy of public scrutiny was that he committed campaign finance fraud with the hush money. Ironically, no pearls were clutched by his supporters over that.