If the MC doesn't try to fool around with Sage after Chad comes to her for help, she will tersely kick the MC out. He will have no real interaction with her through Episode 4, and the episode wrap-ups will say how Sage seems to have lost all interest in him.
Come Episode 5, Sage will still give the MC the speech about how Rusty is living in a bubble. But instead of having sex on Tybalt's bed, she will say that they should hang out more. The MC will explain he didn't want to get in the middle of all her drama with Chad, but will offer to be her friend only. She will say she doesn't get rejected very often and admit she is surprised he isn't interested in her.
They decide to leave it at that, and the MC will not give her a guitar lesson after leaving Bella's.