We're going to see the hottest scene with Natalie. For this relationship, Sophia already has "permission" from Liam, in the form of a threesome's mind game. For me that means touching is allowed, kissing is allowed. As a sister, Patricia runs outside the normal rules of the game.
Sam, on the other hand, is a completely different level. If Sophia allows Sam to kiss and touch, she is actively cheating on her husband. That Sophia fantasizes about it is one thing, but it is something completely different to make it reality. Therefore I think we will see a strip of Sophia in her bedroom while changing her clothes, while Sam is watching from across the street from his room. Even if Sophia knows that he is watching, and also realizes that Sam knows that she knows that he is standing there, she can still credibly deny it in front of others (including Sam).
The Cathy Event will change these rules. Something will happen there or something will be said that makes Sophia believe she can also take away certain freedoms from potential male sex partners (for example Sam). And that's why she won't reject any further advances made by Sam during the next day's music lesson.