As a researcher who has helped folks find those connections that are missing because of adoptions, I can state that you being the Mom that raises him will always be the Mom of his heart.
With that said and out of the way he will be torn with the loss of information (those same questions you are having now), if the adoption records are open he will be able to read about himself, a better solution would be for you as his Mom to be willing and able to help him when the time comes that he is ready for that knowledge. There is such a bonding that I have witnessed so many times over the years between the child that has both of his Moms being open to giving and receiving of not just the information around the birth but sharing the joy of having all the medical information readily available (not something a young Mom thinks is needed for the future adult that baby will be) and maybe if both sides are comfortable with it a sharing beyond what is normal in most adoptions.. An open adoption can benefit everyone in the triangle.

One Mom gave birth and loved him enough to hand him over and the other Mom gave a stable loving home, there is so much joy around a baby and they should always understand the sacrifice that birth Mom gave, it is not an easy choice for many to have to give their babies up and the knowledge and understanding from the Moms on the role each has played will go a long way in raising a human that is grounded in love.