Well while communication works for everyone, some people have different levels of communication. Keep trying to open the communication but you may find he is being very introspective. I know when I hit that type of wall I close down externally. I didn't even know I was doing this until one day our ex told me she knew I was "thinking" because of how closed I was. Damn I need to be careful sometimes.
When I was closed, I decided to write. A journal. This helped me clear my head and in turn, I could let my wife read what I thought she needed to.
Assuming he wants a DADT situation could be worse than continuing with the status quot. If he hasn't responded poorly to hearing the day to day life with the bf, then keep going. He may just need time to stew in his own thoughts.
Your statement about being able to find someone better suited and that causing a breakup is an odd one. I don't think I have ever read anyone that is poly say this (I have only been reading on this for 6 months). You love you SO, finding someone as a better fit would simply expand not destroy, in theory. I find it interesting that you mention that.