Helping my SO

SO and I have been together for 3 and a half years already. For the past year, I would say. His drinking and smoking (cigarettes) has gotten out of control. We had a really deep conversation two weeks ago and he confessed he wants to stop and be like before. When I met him he was all about being fit, he would eat healthy, drink occasionally, smoke never, he had a nice body and now all that went to the trash. He has a rookie beer belly, smokes and drinks almost everyother day, and last month gave his last payment for the gym. Today he told me he's going fishing with the guys, he wants me to keep texting and calling him and telling him stuff so I can help him control himself. What can I be telling him? I was thinking of even sending him a picture of how he looked before and see what he sends me but idk. I've never dealt with anything like this. Help please :(