Usually someone who is addicted doesn't know they are addicted until they started affected the next people around them, and again when they found themselves too much attached to what they are doing or and can't limits and take break from gambling then we should know they are addicted to gambling which is tantamount and equivocally of seeing the therapist for a solution and remedies.
It plays out that way for some individuals, that it would take the next person close to them to call them out on their shit before they realize just how deeply addicted they are. For others, they would understand it from the point of having anxiety over the game. When you just don’t play or haven’t play, you feel like you are missing something, like a win is about to pass you but when you just don’t win everyday. When you recognize this, then you would know their is an addiction problem looming.