The game is incredibly good and the art is amazing, but like other people are saying here, that NTR scene of Lily with your stepmom feels out of the blue, specially on a playthrough where I'm devoting to Lily. It makes no sense.
Someone else said that the key to not trigger this relationship is to scold Lily when she is complimenting your step-mom, which is great to know, but it is absolutely counter intuitive, because what you do on that scene is saying that Lily is right and you start complimenting your step-mom too.
Edit: I tried to scold her but it didn't change the outcome. No matter if you scold her or not, she cucks you there with your step-mom. Definitely it makes no sense whatsoever on my playthrough.
If anything, the choice hints that you are open to have something with your step-mom, rather than Lily suddenly cucking you.
That said, I want to stress that the game is incredibly good and the art is amazing, and this is the only problem I found on a so far incredible experience. Just a question, is there an update walkthrough? I tried to search but only found a walkthrought for a little bit of chapter 1