Just a thought, but why not start off your letter by telling him you love him and how much it ment to you for being so honest in his letter. That it seems so much more settling and understandable as to what has been going on. Not that it is no big deal but at least he is trying to communicate and still we have to read between the lines.
Know where in the book does it say we can not be understanding, but that is where our recovery comes into place to not be taken, plus it gives us a real good look at where we are in recovery.
Just my belief, but I think our recovery is just as challenging as an addict's recovery...we both have challenging times and when do we both know when we are in a safe ground.
I myself don't think I would respond to his letter in a challenging way....
Rose