There's a lot of light in the room. There's no escaping it.
Nicotine is not a crutch, it's a limp. Accountability is a crutch. Use it to get stronger.
Nicotine doesn't help you concentrate. Your quit mind is nimbler, more curious, more alert and more focused. Inability to concentrate is a side-effect of nicotine use - the fact that you most keenly experience this side-effect only when you quit should not deceive you.
Nicotine is not a drug, it is a toxin. This is what the tobacco companies mean when they deny that tobacco is "addictive". It doesn't make you want to use it, it keeps you from wanting to stop. It's only a collosal mind frack that makes you confuse "keep me from feeling worse" with "make me feel better" - a mind frack that you'll fight against for long after nicotine is out of your system.
You are sucking on insecticide, ammonia and carcinogens. The parts of your brain and body that it attacks make you feel sick, and you realize how sick it's making you only when you try to stop using it. It does not make you feel better to use it. It only dulls your realization of how much damage is being done.
My guess is that these things are also true of nicotine's contribution to your life as a student:
Nicotine has kept you awake when you needed sleep.
Nicotine has disrupted your healthy eating habits, which hurts your ability to think clearly.
Nicotine is gradually sapping your energy. You're exhausted when it's time for bed. You feel like crap when you wake up. You don't want to do much during the day.
You've emerged from your shell of self-delusion, turtle, and into the light. Slow and steady, walk this way.