How do you know when someone has a drinking problem?

I would not exactly call it a problem but on the verge of becoming one. I would say this would be the time to get him help as it will only get worse. My step dad was a weekend drunk and a mean one, later on as i became married i learned the one Girl he loved when younger more than life refused to marry him because of his drinking. My Mother was tolerate of his behaviour and i believe loved him as he had loved the girl he lost. Explaining why she tolerated his drinking binges. But he always kept a Job as he never drank during the work week.