Off the top of my head, some of the major sex-related ones are: Lesbian(Maybe), Threesome(FFM), BDSM, Probably some Femdom/Maledom(Fairly tame, most likely), Masturbation(Male and Female)
And just in general: Multiple Endings(Eventually), Occult themes, Blood/gore/violence(Likely nothing over the top). There will also be some themes of sexual violence and suicide mostly having to do with backstories and whatnot.
What there for sure won't be: NTR/Cheating
I hope this gives a good idea of what's to come. If you're wondering about anything specific, just ask. I can say if it's planned, possible, or just won't happen.