[[WMG: Robinson Crusoe and Friday had sex.]]
Robinson Crusoe had been all alone on that island for about twenty years. That has to make a person pretty sex starved and not too picky about sexual partners. Then along comes Friday, a young and handsome man who's willing to do anything for him. It would not be surprising if he took advantage of that to satisfy his "needs". Plus, the book is supposed to be an autobiography that Crusoe is writing for the public to read. It makes sense that a man in eighteenth century England would conveniently leave that out.
* While it's true that older works (generally nineteenth century and previous) do describe close friendships and even familial love in language that sounds romantic to us, I have to agree in this case that the HoYay is too blatant to be attributed to HaveAGayOldTime. The very first thing Crusoe says to describe Friday (while he's sleeping naked, no less) is that he's a "comely, handsome fellow" with a nice-looking body.