I think it's a matter of perspective that Lena cheating on Ian isn't that crazy, she's just a woman with a very high libido, the craziest thing in this story at the moment is Seymour who is a rich man with a sick obsession for Lena.
And I'm not denying that they do more depraved things especially because Lena will probably be involved in a porn movie because of Billy's contract, but nothing as ridiculously crazy and stupid as all those who masturbate thinking about Lena being sold to a sheik in dubai, because that would be shitting on a very good story just for the pleasure of a few.
In short, it's great that there is sex, hot stuff, tattoos, lewd clothes, that's why we like this game apart from telling the story, but all within limits that do not lose the verisimilitude.