I have been knowing my friend for 11 years and lately he's been getting into the habit of drinking more than 3 beers a day...

He has a baby and a girlfriend.. and I believe the alcohol is influencing him to cheat on his partner. Yet he says he loves her.. He has told me, he has bought girls over.. and it sucks knowing his girlfriend, doesn't know.. I want to tell her but at the same time, I feel like he should let her know.. At the same time, there relationship is weird. It's like they are together but they always argue and don't appear happy.

He's always tired and looks numb.. I try to talk to him saying, it's poison and it's bad for his liver but he says "who cares. I like it"

Is there anything I can do at all?