I think at this point you must apply Occam's Razor. It seems more likely that Melville was having fun and subtly hinting at the homoeroticism of the situation. Otherwise, you are indeed "consciously working to not see", like user nemo said above.

“It seems more likely”… based on what? From the perspective of modern repressed culture? It may indeed require conscious work to look past that.

Could be right, could be wrong, but the gp seemed to be dismissing even the possibility out of hand.

I don't know if it was common or not.

But let's not forget that until recently heating was extremely primitive, houses had almost no insulation, and European winters seem to have been colder and longer-lasting.

Staying warm and dry was a real problem, and it wasn't unusual for families and sometimes friends to share a bed because of it.

There's probably a PhD waiting for someone who can write up a thorough survey of the effects of improved heating and lighting on relationships and sexuality.