How can I quit when smoking calms me down?

Find healthy outlets. There are lots of ways to calm down, usually when you are addicted to a substance such as nicotine it seem like the only solution. People without addictions need to calm down also, they may call a friend, go for a walk, meditate, etc. See a doctor for possible use of meds to help with cravings, then find "healthy" habits to help you calm down, it can be done!
See below. You forget. The nicotine withdrawal is the reason you need calming. When you are completely over this withdrawal, the need for calming is far less.