Do you feel like involving yourself in this? Is it in your best interest? You have been separate for a long time. I think these are questions I might ask myself if I was in your situation.
If you intend to be supportive of him I hope that you will go for the counseling that is being offered thru the rehab center. I am sure that they can provide valuable information on how to relate to him and what is helpful and what is not.
I am sure that most people who are getting clean go through some pretty heavy changes. Maybe if you went to alanon meeting they could help you sort out how you feel about facing all of this and your motivations behind wanting to involve yourself in his recovery...