What all do you need for Cain's best/romantic end? I remember from before the updates and then tried to follow the new guide, yet it defaults to friendship with all the guys end, even if I find the notes in the study and such.
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Mostly you need to make sure intelligence is your highest stat (by going to the library). Studying the vampires gets you a chance for a scene with Cain, so follow him. After that scene, however, it doesn't matter which fae clan you study. The other things you'll want to do is get your magic high enough that Cain doesn't die, and text him as many times as possible. Be sure to rest (in the lounge) before your stress maxes out (I usually rest when it's at 18/20). It's not necessary to go outside or to the pool at all while on Cain's route. I hope that helps!
Edit: I just remembered--click on the heart to check your affinity with him. When it's at 13/15, you're pretty much guaranteed his best ending.