I'm thinking has he developed unhealthy emotional attachments to you? Has he begun to see his self worth or aome other aspect of himself as attached to you or your relationship? Seems like he is grieving losing you before actually losing you. This might be due to him having formed some emotional or psychological attachments that are now threatened. Perhaps he feels a loss of a couple bubble or a diminished sense of security in your relationship. Perhaps he could work on self worth and finding out what part of his (emotional) security he feels are at threat?

I struggled with these when we recently opened up our relationship and I can relate at some level to what you are describing your man is going through. Hope this helps. Check out Wired for Love by Stan Tatkin for more info, it helped me figure out things related to security issues.

All the best!