If it's mutually decided then it's clearly not deception, and whatever floats your boat, tbh.

Your other responses referring to evolutionary psychology, the chance of altruistic friendship etc. etc.: there is a difference between the evolutionary fact that your inclination to be friends with someone will be based on ultimately selfish goals, and being selfish yourself. The psychological make-up we have is a brute fact of existence and we need to take it into account. But selfish genes do not mean that the concept of human unselfishness is a busted flush.