What is actually going on with Sierrah?

I understand that Billy wasn't really being particularly sexy when he gave her the oil massage but he might not be used to performing on camera seriously. And maybe the sex wasn't incredible the second time, I don't know, when you don't know each other very well it can be a bit awkward, just communicate that so you can work on it together. But to confide/have an emotional if not physical affair in Adrian? Really? He can barely string a sentence together and is completely dismissive of women in general. She just seems so off in her actions, like she seems like she straight up hates Billy at this point, what are we missing?