Mmm. It’s not quite as simple as that though is it? In one way it’s not our concern, but in another way they make it so by inviting the public to be part of their births, marriages and deaths. If the public weren’t interested in their daily lives then the monarchy couldn’t really exist.
You can’t say that an affair is entirely unrelated to a Royal marriage and their children either can you? And if it is the heir to the throne’s marriage that is affected, then that could well have implications for the institution of the monarchy, which would in turn make it the public’s business.
This is where hypocrisy arises when they allow the public to be part of the happy events, and even the sad events if they are respectable, but anything unsavoury or unpleasant is covered up. It’s all smoke and mirrors tbh.
I doubt we will ever know for sure about Rose Hanbury, but I think it’s quite likely that William could have an affair, simply because he has grown up with his same sex close relations, his father and grandfather, doing the same. The aristocracy have far more time and opportunity to have affairs than ordinary people, with ordinary jobs and families living in one home.
And I imagine that, just by dint of the fact that he is the POW, he would have a raft of aristocratic friends willing to smooth his way, or provide bolt holes, in return for royal favour.
Kate is an intelligent person and she will be aware of all of these issues. I am sure she knows that the continuation of the British monarchy is almost totally dependent on her and William’s marriage thriving. And as pps have said, she hasn’t put a foot wrong so far, so I doubt she would be blamed if it didn’t! Especially given the RF’s past track record. That leaves her in a very strong position indeed. A very stressful one too.