I might be repetitive, sorry I don't have time to read the other posts right now.
I think if I were you I would tell him with as much love and caring as you can muster that you think you might be poly. Tell him about the two other men, tell him that you do not intend to cheat or pursue anything that he is not able to handle right now due to his circumstance, but that you have given it a great deal of thought and that it will come up one day.
Then let him do the talking. He might not be jealous, but it sounds like he might be concerned that you will leave him... keep reassuring that is not your intent, but you don't know what will happen... no one does, EVER.
Then I would direct him here there and everywhere on the topic of poly and leave him alone with it for a set amount of time that the two of you agree on... or decide to investigate together... the idea being it be how ever he wants to approach it for now.
Remember that you have lived with this for some time... respecting that he needs to catch up and learn is important for your future with him. Thankfully there is no real possibilities on the horizon right now and you haven't cheated... that is a HUGE bonus. Take your time, let him take his time. I would think that getting this burden out and off your shoulders will make a big difference to you.
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