But in the beginning Sophie never thirsted for Zack's looks, and Zack is also a playboy, she sees him fuck other girls multiple times, and its also not like Zack particularly likes her personality but he is more obsessed with the fact that she does not thirst for him like most other girls, it is his main attraction to her.
The fact she talks about him and his looks as often as she does in the way she does shows she is impressed by it. If you aren't impressed by something or if something doesn't matter to you it's literally unremarkable. You don't remark on it at all. I think she recognizes the temptation she's feeling and tries to talk herself out of it.
I also found it interesting that when she thinks about the way Amy is dressed or acts she frames it mostly as Felix wouldn't like this and Felix would object rather than what she thinks about it. It shows a couple of things, one is she is compliant and subservient (opinion wise) to her "man" and she, if she were on her own, thinks of things differently than Felix does.
I also think Zack has 3 motivations.
1) Fuck Felix over for 'standing up to him' on that first day.
2) Sophie is hot as hell.
3) Possible Mommy issues, we'll see though.
This is all dime store psychology so I recognize I could be wrong.