alcoholic friend

🍁🌿🌲🌻
One of my SO's best friends is dating my cousin. His friend is an alcoholic and my cousin is still very young, too immature to be in a relationship with this many issues. They are both really great, big hearted, and hard working people. They help raise my younger cousin because my aunt is a single mom and works crazy hours most of the time. 
Last year they started becoming physically abusive to each other and the both of them lie about it. 
We have been trying to be supportive without pushing them away from our family and making things worse but we do not support their relationship as it is now. 
My cousin recently broke up with him and has been seeing other people, yet she is still messaging him saying that she loves him etc...
He is drinking heavily and refusing to go to rehab unless she promises to stay loyal to him while he's there, but this has happened before and it hasn't lasted long. He is threatening suicide and everyone is worried.
We don't know what to do at this point. I do not want my cousin in a relationship with him and I do not think it's fair to ask her to be loyal after they broke up while he's in rehab after everything they've been through. I want him to let her go and realize he needs help and want it for himself. Drinking aside, he's an awesome person. Do we bring him to the hospital and show them the texts to prove that he's harming himself and mentally unstable? Will they put him in rehab?
Sorry for the long post, we are just at a loss