My ideal for a sequel (ITS GREAT)
So, David is back home and everything is normal.
Then, his parents get depressed, get divorced, his mom becomes alcoholic and dies from liver disease.
But here's the thing - David knows that in the parallel world where he went missing, his parents, in mourning his absence, were still together.
So he gets hit with this dilemma - that if he had disappeared, they would be happy and together, but when home, things take a turn for the worse.
His guilt/shame lead him to turn to meth and other drugs, and he eventually gets stabbed by another user.
Pretty cool, right?