I don't think your parents are going to believe your stupid enough to believe there is nothing wrong if they are sleeping in separate rooms.

I would call them out on it.
You have to live there too.

Quick point, I couldn't sleep in the marital bed when my partner wasn't there. So if I was ill and he slept in the spare room I would sleep on the sofa.

I Sure I am not the only one with these quirks.
Please talk to them Art, th nightmare we create in our head is,always worse than the facts faced in the bright light of day.

You need facts, you can't build a coping mechanism on foundations of sand, which is what this would be, a constantly shifting situation of your making.
And to be honest, your old enough to be included in the conversations they are having.