Cravings - How do you know when you're becoming addicted?

[blahaha]

Swim has been thinking a lot about this question a lot lately. It would be pointless to ask how long it takes to get addicted, there are too many variables. Swim asked people how long it might take and got all kinds of answers ranging from the first use ever to a few weeks. Swim would just like some information on how to recognize addiction creeping up. Swim has been getting high for a long time but has never had cravings or withdrawal of any kind.
Where is this addiction people speak of? Do you have to be really heavy into the drug? Do you have to shoot it? Swim just wants to know so he can stop himself before it gets out of hand. He doubts it will though.


A little about swim:
He only does about .1-.2g before college 2-3 days per week to help him study. He makes bad grades without it, lol. College is boring shit.
He does .25-.50g about every 2-3 weeks.
He never shoots it, used to smoke it, now he snorts it.
He usually only stays up 2 days and makes it a point not to go past 4. Only been to 5 days one time.
He's been on that schedule for like a month now. He's been getting high with a few weeks to sometimes even a few months in between for almost three years. Not counting the times he only did a point or two to help study, he's probably gotten pretty high at least 40 times.