Maybe his comments about drinking again are nothing more than his way of saying, "I'm having a bad day."
Keep the lines of communication open... try to be supportive and just listen. I think it is good that he is talking about his feelings to you. I wonder if he has an AA sponsor.
If a relapse happens, it happens... but it doesn't have to be the end of the world. He can come through it again, just like he did the first time.
Thinking of you.