I could have been clearer there. I should have made a clear cut distinction between "RELATIONSHIP" - the thing with cuddles and dinner dates and roses or whatever - and "Friendship" - sort of occasional common endeavours like putting a new manual boost controller on your turbo or sorting some harmony songs or running a CAT5 network through the house or driving you back from an operation when anaesthetic would make you unsafe to drive, etc.

RELATIONSHIP it seems to me must include sex (in the absence of relevant physical disability and there are of course many ways to skin cats).

Friendship - well, a male/female friendship can be a nice luxury if you are getting all the sex you want elsewhere. Otherwise Nicholas Monsarrat had it right "No man ever meets a woman without measuring the sexual potential between them. It may be zero, but he still measures it". I can think of one woman on with whom I get, and we have (I think) a good friendship because while many think her very attractive she is about as far from my ideal of sexual attractiveness as possible, and apparently I hers. That works too. But if that attraction is not zero a long-term close friendship is unsustainable