I mean, it's not really railroading when the player does have control over whether Cindy looks for greener pastures, and the main complaint is that it is perhaps not telegraphed in 100% straightforward "she will cheat on you if you pick this option" manner.But you're right Eva Kiss generally includes ways to hop off different trains and doesn't railroad the player into getting cheated on.
The way to hop off here may very well be option for Ian to break up over this. (or to decide that he'll let Cindy walk all over him as much as she wants) Similar to how Lena's cheating is dealt with.
... maybe we'll get a Punish Cindy scene.