Serinus

The mother absolutely knows.

She may be in denial and go through hoops to rationalize it, but deep down, she knows.

Do you know how scared he'll be of that cake regardless? Kind of hilarious if you imagine him grabbing it from his wife to throw out.

They live in the same house and it's been going on for years.

Adult daughter comes home and spends the night in the same room as dad on a regular basis. How many times do you think that can happen without the mom having a pretty good idea of what's going on? (Even if she doesn't want to admit it.)

Food and lodging are likely absurdly cheap outside of Europe and the US.

And I expect most of the time is camping.

OP's health issues likely contributed to less camping and more lodging.

But it's likely all the extra flights that cost so much. And the trip to Antarctica can't be that cheap.

Well, the payload is also changing all the votes.