would you tell the exwife?

i am engaged to a guy who has a 13 year old from a previous marriage. He has a drinking problem. He drinks many nights during the week, and gets hammered on weekends. We bought a cottage next to his dad and brothers. So every friday night he heads to dad's cottage or brother's cottage and starts drinking. Neighbours drop in and he talks to them and has more beer. Stolls in at 1- 2am. Does the same on Saturday, only he starts at 2 pm. Sunday, he starts drinking again at noon, and then wants to get in the car and drive. He has his daughter one week on, one week off. I live with him part time as well. So the weeks he has his daughter, I live at his house. The weeks he doesnt have his daughter, he is supposed to be at my house. He often does not visit me, as someone dropped by and he had a few beers, or he is exhausted on the Monday from partying all weekend. He is 46 years old. I have been trying to get him to get his drinking under control, but he won't get help. I have made his problem, my problem, which is not good. Anyway, his drinking is now out of control, and he was binging for the last two weeks. First week he was pissed at work, and drank. Then he found a new job (he is union), so quit his job and decided to take a one week holiday. During this one week, he drank everyday. Drunk on the Tuesday and Thursday nights. I approached him on his drinking and his reaction was brutual. Even after this discussion, he proceeded to continue drinking on the Friday.

As a side note, his daughter arrived on the Friday night after school and was sick. He decided to stay at Dad's house drinking while I was at our cottage watching her. He strolls in at 1:15 am and gets into bed. Does not even check on he. I was pissed. I have told him it is over, and am worried for this child. Would you tell the ex about his drinking problem? I think she left him because of it, but his friends and familiy will not shed light on this.