It's a tough conversation to have. I've had the same conversation with 2 friends of mine. When I spoke to them about it I would be up front that I was "sounding like a broken record" but I was only telling them this because I was concerned. My one friend was pissed at me, but she then eventually went to see a therapist and thanked me for my honesty (that took a year)

Perhaps setting a time line on it for yourself i.e. I will speak to him about it and then give him 3 months to start showing some changes. Otherwise I think it becomes a never ending issue with no end in sight.