Can quitting smoking (tobacco) cause you to go into depression?

Possibly. Nicotine is a stimulant drug that speeds up the nervous system. It is considered a behavioral stimulant and is highly addictive (as you are well aware). In addition, smokers often stop taking their frequent relaxing breaks when they quit smoking. Both the withdrawal from the stimulant and the cessation of the frequent enjoyable relaxation can lead to a downward emotional spiral for some.