I really agree with the posts above. It’s nice to see well written criticism.
My ideas that could improve the story and make it hotter would be:
1. Make it more difficult for Sophie to fall. Don’t make Zach better than Felix in everything. Sexual prowess sure, but not also in physical beauty, charisma, emotional openness, being a romantic, having a better career (Zach’s possibly future NBA player), etc. all at once. It would make the struggle for Sophie feel more real and would give her some difficult decisions to make. (“He’s good in bed, but not much else… Is this worth it to me?).
If it were like this we also wouldn’t need so many remainders how Sophie feels pity for Felix or how she regrets sex with Zach. She could enjoy the sex fully and still have a dilemma to solve.
2. Have Sophie genuinely try to keep her life with Felix going. Instead of replacing Felix with Zach so quickly, have a period where Sophie’s having a functioning life with her husband AND having an affair with Zach at the same time. You know, like real affairs usually go. This would have made it more realistic but also open to much more organic situations for Felix to get suspicious than getting Zach’s videos and pictures. This “affair period” could have lasted for months.
Imagine if Sophie kept having regular sex with Felix while having an affair. We could have Felix slowly getting a feeling that he’s not satisfying her in bed and maybe trying his best to improve himself. It would make it much more tragic if Felix was somewhat average, trying his best, improving himself and still coming short against Zach. Sure, go wild at the end, make him pathetic etc, but there was (and is) a potential for so much more than “loser has no chance against an ultra chad”.