Marco,
The short answer to your question is - there's no way to tell whether you are an alcoholic based solely on the amount/frequency that you drink. I would say that you are a moderate/heavy drinker when you drink. he difference is not the amount, but what's happening physiologically when you drink that makes someone an alcoholic. Alcoholics are genetically predisposed to the disease before they ever pick up a drink. The progression to "can't hide it anymore alcoholism" is identical to the life of most heavy drinkers... untill the alcoholic tries unsuccessfully to limit or halt their drinking.
See if you can pick up a copy of Under the Influence by James Milam. It does a good job of explaining the progression in alcoholism and the difference between alcoholic and non-alcoholic drinkers. Check it out online at amazon, you can read the first few pages to get a feel for it.
Good luck!