First: I notice that you've made no effort to refute my claim; you've changed the subject instead. So I'll ask directly: if polyamorous relationships aren't about sex, then why not simply have friendships? If sex was absolutely out of the question in any polyamorous relationship, how would they differ from any other deeply intimate friendship? (ETA - intimate friendships have changed over the centuries; things that we would consider bordering on sexual without being overtly sexual were much more normal among same-sex, nominally heterosexual friends up through the 20th C.)

Second: Yes, arranged marriages (and political marriages fall into that category) are entirely about sex. Or, to be more complete, they're about producing children that have a specific parentage, which generally requires that the two people have sex. (Adopted children are not usually considered an acceptable substitution for blood in arranged marriages. Similarly, the children of concubines do not have rights of inheritance.) Charles was expected to marry Diana and have children with her--which absolutely meant that he was obligated to have sex with her, even though he and Camilla were very much in love with each other--in order for the royal line to continue.