Addiction is a disease that affects your brain and your behavior. You have control over your choice to start using drugs, but once you start, the pleasurable effect of drugs makes you want to keep using them. Over time, your brain actually changes in certain ways so that a powerful urge to use drugs controls your behavior. This is what it means to be addicted to drugs. Someone who is addicted uses drugs without thinking or caring about the consequences.
The first step in breaking addiction is realizing that you control your own behavior. You can't control how the people around you act. But you can control how you react. It's the only real control you have in your life. So use it.