ohh fuck, but i logically it will not "secret" anymore if MC's break up with Layla, maybe Alexis will be more direct instead of secretive (i hope so)
The idea that you breaking up with the girl's sister and would cause her to excitedly go "does this mean he's single now?" with jackpot eyes is AVN logic

In the real world this girl should support her sister, and go a bit cold towards the guy that hurt and left her a crying mess.
ASP is a path where Alexis has a schoolgirl crush for this guy that keeps building and building...
She keeps running into him, at her house, at the bar, at college(?), and since he's "part of the family" their interactions are nice and friendly, full of jokes and teasing... this keeps feeding her crush, her desire... until it errupts someday and something really wrong happens

By breaking Layla's heart, you are not gonna be invited into the house anymore, and it's probably gonna be a little awkward when she has to serve you drinks... you lost the means to keep feeding her crush.
At this point you are off both on ASP and Alexis normal path... so there's nothing ahead... unless Nyx creates a 3rd Alexis route.
And i don't know if a 3rd route coming out of ASP is a wise move to be honest.
If Alexis were to get a 3rd route the one that would make the most sense to me is a comeback route where you banged her a couple of times early in the game... and then just stopped, no fights, no break ups... just stopped.
In this situation she clearly looks sad everytime she sees you, like she's hoping she could get another shot... at least to me that's the one that makes the most sense.