Ok, I really wish I remembered more of this movie BUT what I remember was it was a sci-fi movie (either American or possibly British) probably shot in the 1990’s or early 2000’s where much of it takes place in an apartment complex. There’s some sort of mind altering agent involved that is slowly altering the tenants minds/personalities. The main character becomes slightly obsessed with one of the women living there and in one scene he follows her to a rave-like party happening in a cave-looking environment. I think the girl kisses another girl on the couch at the party while this guy watches, that whole scene was pretty erotic and the song that was playing was great… sound familiar to anyone??