If you feel the need to do so, sure, tell the guy you are concerned about his drinking and that you hope he will get help for it. Just don't delude yourself that if you say it JUST THE RIGHT WAY, he will take that and run straight to rehab or AA.
Unless he was already thinking about quitting and on the verge of doing one of those things, your words may ease your conscience but are likely to roll right off him. He might even thank you and say he's been thinking about it, which might stir up hope in you. I wouldn't believe it unless he actually DOES those things. And given your emotional attachment at this point, I wouldn't be surprised if you keep hanging around, hoping he'll see the light. THAT could be literally years or decades away. And in the meantime you would be wasting your time and your life on someone who is completely uninterested in what you're waiting for.