I think looking into a temporary guardianship is not a bad idea, if you don't mind looking after her (and it sounds like you don't and you are glad to have her in your life.)
It sounds like this guy is really tumbling all over, doesn't it? I think drinking is always bad news. I had friends who would do cocaine now and then and only because they were drunk and wanted a "pick me up." Being drunk also leaves you without any common sense, so of course, you're going to do stupid things.
I'm curious, what is his ex like? Is she still in his life much? She doesn't have custody, right? Is she someone you could talk to? Or is that not a good idea?