Dear Simon,
it is NOT your fault that your parents started to drink.
It runs in families and genes and environmental factors from their past, they certainly have had problems in their life which have nothing to do with u. Not being the "good boy" is actually very healthy response because when things aren't right surely someone will start to have symptoms - and usually it's the kids. And parents won't see anything wrong with their lifestyle. But I know it can be very emotional issue and hard to rationalize. You are very special and that is for sure. There's no use to feel guilty, but I feel for u, I feel guilty easily too. It's nobody's fault that ur parents started to drink. U have the right to not be that "good boy"
and have the right to express ur feelings and angers. Hope ur mood lifts soon!! ~Hugs~