No, not unless he had a good and convincing reason to ask me to quit gambling.

Just because he is my friend does not make his reasoning correct. And he would have to convince me of that reasoning in the first place, so I would consider it at all. Because I do not enjoy being told what to do unless it has good reason. A lot of people exist in the world and each has his own morals and ways of living. Some people in this world want to be able to tell anyone what to do. But that is not right. Everyone has to be able to make their own, informed choices. They can try to talk to them and get them to see their side, but that is it.