the good ending is where you knock on may's door, maybe a couple times im not sure until she answers, and then convince her to talk with you. talk about the most serious stuff. then, go to the bathroom after.
also, it's kind of funny how i got the good ending on the first try. great game, though.
EDIT: the time matters too. look around the room and hear whats being talked about until like 2:10, then when you click on may's door you can hear her mom screaming at her.
an hour later, at around 3:10ish or later, you can then knock and start the dialogue.