It must be difficult for you. Why did you commit to such a relationship? Even I, as a mono would not entertain a long distance relationship. I can see that for a poly to be in a relationship with a mono would be hard enough, but long distance? You must be getting something truly amazing out of it.
I'm mono with a poly partner and I have chronicled my journey of coming to acceptance. You might want to point your partner at my blog, it could help him come to understand you.