I believe that with everything they experienced, that is the natural and expected reaction. In the bathroom, Aron thought he could have something with Sara; upon seeing Sara refusing and rejecting him, he simply lost control. If he couldn't have Sara the easy way, he would do it the hard way. At that point, Aron had no options left. Even when Sara discovers that her son knew, she starts lying and saying it was only once and that her relationship with her father was over, hiding behind excuses and not wanting to accept her responsibility. Let's remember that David even went to Sara's room with the father next to him; Sara and David didn't care. David even mocked the father and compared himself to him. It's not surprising that Aron is doing the same, but this time comparing himself to David, trying to surpass him and be better than him. The plot will revolve around Aron fulfilling a mission that was originally Peter's. In Peter's final scene with Sara, he mentions that from now on she will be satisfied and that she will no longer need that brat, referring to David. Aron will take on Uncle Peter's mission: to satisfy Sara, even if she refuses and avoids being alone with Aron. He will find a way for it to happen, just like Daniel in the early chapters. Aron is quite lucky; David will be busy with Alice, and Peter won't be able to approach her with Aron in the house. The only available man is Aron. Sooner or later, she will seek him out on her own, just like Lana in the recent chapters.