Now that reminds me of a certain Lamia from a certain D&D campaign I played in the past... Boy, that was truly kinky...

Anyway, stopping with the random deviations and jokes, I'm pretty sure that their demonic forms don't play that much of a role in a relationship amongst Demons, as each reacts differently to the energy present in the underworld and have a human form that is far from being a mere facade. In fact, I'd say That relationships in the underworld would be most likely related to mutual benefit or strong emotional bonds rather than appearance. 

Also, Snakes are hot asf. Kek