Well - do you find it a hurdle to being together now? If not I wouldn't go out of your way to learn too much about poly if you aren't interested in exploring sexual desires or romantic desires with other people. It is natural to worry if you believe he thinks relationships should be sexually and emotionally monogamous, but people often make statements about "this is what I think" and if you ask them more questions find there are all sorts of grey borders and exceptions to what they really feel - maybe he has some of those.
I think if you are happy and content being ..nonsexually monogamous with him, it should also be easier to bring it up with him since you aren't asking for any changes in your current dynamic, just discussing a topic for the sake of discussing it. The fact that you are nervous to bring it up does somewhat imply to me that you are not so sure this will work long term for you, usually for me at least, being nervous is correlated with hoping for a specific outcome.
Happiness will never come to those who fail to appreciate what they already have.