Hi Lou - on the heels of Gwen's very wise post, my advice is to prepare to see some immature and very odd behavior. I think this is where you will need tremendous patience and really rock bottom expectations. I can only imagine that you both will need a hearty dose of time and space from each other despite living together.
As my h is a live-in I try to post a lot about what I am seeing and hearing so that those with limited contact or with vanishers don't go down the road of thinking that their MLCer is some sort of new and improved version of him/herself. These people developmentally regress in all ways.
According to all the reading I have done, when the MLCer comes home it is merely the end of the beginning of his crisis. Crazy, warped timescale, I know. I often picture flipping an hourglass and having one grain of sand come down over the period of a few days. It passes so slowly, you're not even sure it's really moving.
You have raised teenage boys so you know the time it takes for them to grow up. I have an almost 13 year old and I now see so many similarities between him and my almost 50 year old MLCer.
Thankfully, your h has already been doing some work in himself through IC. Long groan on this one, but, I am sure it comes down to tremendous patience and no expectations.
Thinking of you.
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced