Kim, It's certainly your choice to tell him or not. Do you think if you tell him now or he finds out someway, somehow in a year or two, that it would be better?
I was trying to think how I would react to that. My H had the A, if it had ended but he didn't tell me, but I found out some day, would it be easier to take than me finding out about it before it was over? Probably because I wouldn't have to go through the pain of living with OW in our lives. But it would still hurt.