Tell him. If your behavior seems to contribute to strain in the relationship, it would help to explain it by telling him. That way, he can seperate confusion of facial expressions or interactions from YOU, in other words, he won't have to wonder whether to take it personally, as I am sure he is confused about right now. If you've been together so long despite the challenges of AS, I am sure that telling him about the AS will make the relatinoship better! He is not going to leave now becuase you told him, but if you don't tell him, it's possible that may happen down the road because he gets confused.
I understand your feeling awkward about talking about it. That's natural right now, becuase you only discovered it recently. Give yourself some time to get used to the idea of having AS before telling him, but with the definite goal of telling him by a certain time. That way, you will be preparing yourself to be open about it as you come to terms with it yourself. Rather than trying to come to terms with it and feeling like you can just keep hiding it forever.