A 'binge' is a short period of excessive indulgence. It usually refers to alcohol or food consumption. The word 'spree' is a similar concept.
Someone who engages in binge-drinking may have significant periods of sobriety, which might last weeks or months. However, that person may consume an excessive amount of alcohol in a relatively short period of time, such as an evening or a weekend.
Yes. If you only drink when your out you have some sort of social problem.