Your situation is not an uncommon one here - it sems that many people discover there poly or bi side later rather than sooner (although that was not the case for me). So I would recommend scanning through a bunch of threads in the into forum and see if any of those resonate with you as well.
One suggestion that I have seen is watching a movie or TV show with a poly or bi theme or character (that you think he would enjoy otherwise) and then initiating a conversation. "So what did you think about x?" You could then see what position he was starting from. You could come back with "You know, I could actually understand x, because I have noticed y about myself in certain situations." And see how the conversation went before you decided how far/deep to go.
I think that the sooner you can bring up your curiosities the better. If you come to him later and say, "I have done ALL this research and discovered ALL of this about myself." He may very well feel blindsided. Whereas a journey of discovery that you can share together: "I had these feelings the other day, and I was scared, so I did a little research and some of these things sounded like me. What do you think?" may be less threatening as it won't be like you are demanding to act on them RIGHT NOW.
Me: poly bi female, in an "open-but-not-looking" Vee-plus with -
MrS: hetero polyflexible male, live-in husband (22+ yrs)
Dude: hetero poly male, live-in boyfriend (3+ yrs) and MrS's best friend
Lotus: poly bi married female, "it's complicated" relationships with Dude/JaneQ/MrS (1+ years)
+ "others" = FBs, FWBs, lover-friends, platonic G/BFs, boytoys, etc.
My poly blogs here:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe