No one really knew about my substance abuse either. Every once in a while a friend would comment on my drinking or ask me how much medication or drugs I took - but they never seemed very concerned.
A lot of my drinking in the beginning was with friends who also drank a lot - but somehow I always drank more. Sometimes I would only bring a little money so I wouldn't spend as much - but my friends would tell me to bring more money because I would beg them to borrow some to get another drink. We were all young and for some reason it's acceptable to do crazy things when you're drunk and young. Thinking back I was the friend who got kicked out of bars, yelled at random people and told my friends horrible things - but for some reason they put up with it, and still enjoyed going out with me. We even joked about it.
Towards the end it was less obvious because I was drinking alone. A lot of people are really surprised when I tell them I quit and don't quite understand the severity of it.