Just say no, if he is abusing alcohol that is reason enough. If you drink, you can't tell him not to, but if you do not drink then get a lawyer involved to block a 10 day visit. I get that he wants to see his son, and has every right at this time since there is no order blocking long visits. Agree to only a weekend, or a three day visit to start and see how it goes with them and the son. If he isn't agreeable to the terms then just say no. There is nothing right now telling you what the rules are.

I would consult with a Family Lawyer on this. Anyone currently abusing substances should not see their child. I would go for full custody.