Ninth House by Leigh Bardugo
"By the time Alex managed to get the blood out of her good wool coat, it was too warm to wear it." Alex Stern elevates from a life of drug use, manipulating ex boyfriends and poverty, to a life of academic pursuit and ghost busting in Yale University. Her unique ability to see apparitions of the deceased (which, as you guessed correctly, is the reason for said drug use), is her winning ticket into Lethe House, one of the secret, supernatural Yale Societies, which is in charge of monitoring all the other secret, supernatural Yale Societies. She has the great fortune of being mentored by Darlington, who introduces her to the mystic world of the societies and their spooky-to-say-the-least rituals and prepare her to, well, basically, be the sole active member of House Lethe when he graduates. There's also a little romance blossoming between them but it's cut short because he disappears -and yet his presence lingers. Most important howe...