Thanks for the chapters, Squiggles & Tomoshibi.
Between BBQ tied hamplanet and his superlatively beautiful mistress, the choice should have been beyond easy. In a manga like this, however--and however unique this manga is otherwise--the MC can't have standards, he's gotta lay anything and everything, no matter how repulsive.
Sao just doesn't make sense if THAT can make him turn away, even for a moment, from Staff--together with Caliba, no less. It's something that deteriorates (if not totally killing) immersion if you aren't simple: when something like this happens, you know it's the author pandering to as many fetishes in the real world as he can instead of writing a story. The story doesn't even have to be explicitly erotic like this one for this to be the case.