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Would you do the same for a friend? Me personally I think I would have just confronted such a friend and told them to seek help instead of me altering my lifestyle for his benefit. If they didn't seek help to the point that it was affecting me I would've just stopped hanging out with them silently I think. A friend would've had to be a real good one to make an exception at least.
If this is a real friend and not a colleague at parties, then why not? I’m not ready to leave a friend because of some problem (which may be completely solvable), and by the way, you didn’t tell in the story, but I can assume that those friends were connected not only by playing poker, right?
It is clear that if my friend has problems with alcohol, then I will not drink when he is with me. This seems logical to me. Same with gambling. It’s clear that he must somehow solve his problems, but I don’t think it would be a big deal for me to help him a little with this.