I slept with my husbands brother!! Now I dont know whether to tell my husband ??

About a year ago I cheated on my husband with his brother. A lot of what happened between us was emotional rather than physical, although we did sleep together on 2 occasions.

I think I did it because I wanted the excitement and as a reflex reaction to being married and suddenly feeling that my freedom had gone, although I still cannot be sure of the reasons myself. The whole thing seems totally crazy now, and I can't believe that I was so stupid. (Although I have to say that my relationship with my husband is now more amazing than ever.)

The problem really is whether or not to tell my husband. Whether I tell him or not, I am 95% sure he would stay with me although clearly if I did tell him he would be devastated and his relationship with his brother would be ruined, although they are not particularly close. Is it better to be honest in this situation, or is it better not to tell him and save his feelings and his relationship with his brother (although it may seem rather cowardly on my part)?