It sounds to me like his concerns are no different than most people just starting to figure out poly. There are plenty of people who get through that and come to realize that usually it is just fine. Marriages end for various reasons... mostly for other reasons than poly from what I know.
I think I would copy and paste, or get him to read this thread. I think you spell out quite well what is going on for you and what your confusion and concern is. Maybe another method of communicating or letting him know that you are so concerned that you are getting advice and support elsewhere will entice him to sit up and take note. It could be the catalyst that you are looking for.
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