Despite no money being handed over per se, sex is still the commodity that's being purchased.
Being someone that's married and divorced twice and have had countless relationships, visits to WLs, Tinder hook ups in between, forgive me for my jaded perspective, but in every situation you're still paying for it, the price (or goods being exchanged) just varies from being ultra cheap (like a meal or drink) to extremely expensive (like eventually taking half your assets).