Hello there,
decisions are meant to be impactful in the game; this is not a ren'py visual novel where you can just "let me go back because I fucked up". The game autosaves at the beginning of the day after the morning interaction and you are able to manually save at the room (it'll be 100 save slots with the new version). You are NOT LOCKED out of seducing Katarina unless you arrest Mario before doing so, as at that point you would be ruining her life, so no, you yourself caused that. You don't need to consult the walkthrough as long as you are paying attention to the dialog, what characters say, and the kind of person they are; if that is not to your liking, this is not a game for you, is just the reality of it.
There is a notebook function, once you wake up, check the calendar the same way you would check a notebook, there are not that many items each day that needs to keep checking. "Cucking" already exists in various places in the game and while not much, there's a BBC scene.
On a last note, is not really grindy, if you do explore and do things you find around, get experience and unlock traits, the game is pretty simple.