Changing his attitude is something I can agree with you in regards to Sophia. However, there's still no reason to think that he will be angry when/if Sophia has sex with Liam, he is his father and there's no hatred or resentment there, granted, so far. First, they have to cross that bridge and then most likely, considering how detailed L&P is being with the story, they will have a talk about what happened and how they'll go from there on, Sophia would talk to Dylan that he has to understand that she is still married and loves his father so he has to come to terms when or if she is with him, those kinds of talks are usually followed after having sex in incest stories. A Talk will be needed and possibly had.
Now, IF/when Sophia is with someone else other than him or his father then, of course, all bets are off, she is his mother Afterall, no Sam or anyone else would have "free pass" to his mother, it's just common sense from a son's perspective in the story.
I liked that example of what happened when Sam was invited to the bikini show. Remember that the idea was his and the bikini fashion show was thought by him for just the two of them, it was Sophia who mentioned inviting sam IF and ONLY IF there're enough points for the player to go with that option, if not then it's just between Sophia & Dylan by default. Also, Remember as per the example, Dylan knows perfectly well Sam's stance and thoughts about Sophia, Sam told Dylan himself in his room after the lingerie incident so Dylan knows that by inviting Sam what Sam would attempt with Sophia and as a son, would you be okay of inviting your best friend to a bikini fashion show between you and your mother knowing full well your best friend's intentions with her? I doubt it.
----I'm liking the conversation here---
I think that might be the point of the fighting lessons, it would make sense, learning to defend himself but against who? Aiden is the only one bullying him so there aren't that many suspects. If he stepped up to defend a weak kid from Aiden's bullying which landed him in this trouble....of course, he would step forward and with a vengeance if he finds out what Aiden is doing to his mother, who wouldn't step forward against anyone hurting their mothers? and with deeper feelings...all the more reason even if L&P finds the time to include in the dialogue of Sophia explaining to Dylan why she did what she did, for him.
Well, you presented three things and I tried to address them with reasons, so I apologize for ranting too much...it does keep the conversation and the thread going doesn't it?
[/ did find out what his mother did the things Aiden