Oh my goodness! Where to even start with how engaging this game is? I've loved reading people's theories for this game so much and I've come up with one of my own. The reason why the girlfriend doesn't (or can't) help with anything around the house is because she's already dead. They had a car accident on the way to the house and the girlfriend died on impact.

Another theory I have is that the MC has been sleepwalking all along - not the girlfriend. And the part where he imagined her hanging out the window and laughing - was actually himself. The girlfriend was the one who tried to approach and get him off the ledge, but he pushes her instead. Leading to her "disappearance" as he buries her body in the backyard and covers it up with all the flowers. Then, his parents call to console him and are sorry that his girlfriend suddenly 'disappeared' - and ultimately leading us to the ending where he feels haunted by her ghost/memory because it's his deep seated memory where he knows he killed her all along.