Hello Phantessa - and welcome.
It's a hard situation you have. In an ideal world we would all 'partner' with others who understood the necessity of each individual's self fulfillment and that the understanding of 'love' was that we would support each other in that quest to the best of our ability.
Add to that the various ways people end up in relationships - particularly married ones - and you find your situation far too prevalent.
When you say he "supports you" - I wonder how much he has truly educated himself on what polyamory is truly about ? There is not a high level of awareness in society in general and a lot of misconceptions even among those claiming some awareness.
My suggestion would be for you both to do some studying together and talking. There's lots of resources even on this forum, pointing to helpful books, other sites etc. If you both were on the same level of understanding it would allow you to have some productive discussions and make some wiser choices as to direction. And if nothing else - you will learn LOTS more about who each other REALLY are - inside. And this may include some stuff you like - or don't. But rest assured, it WILL come out eventually anyway. Delaying it only makes it worse (or delays the positive).