How come you get depressed when you quit smoking?

Is it an actual side effect of nicotine leaving your body? I have quit smoking a million times and usually find myself lighting back up cause I can’t stand the misery.

But this time i’ve lasted over a month. I feel great. I’m not depressed anymore. Tho i’ve had heaps of bad shit happen to me while trying to quit, i’m pretty happy.

But my poor husband gave up smoking 4 days ago. And he’s miserable. Everything to him is negative. I hate to see him this way. I was that way too!

Is there anything to help him not be depressed. Or do you just have to get through those evil 2 weeks without smoking and it will go away. Is there a magic vitiman?