"I just can't believe he things he can hide it...and that I am not smart enought to figure it out...."
Does this mean you are angry? I have had to do a bit of anger work because anger really isn't good for us. I understand your frustration but honestly, is what he has done worth you sacrificing your peace and serenity? Would you be as insulted by a small child who has snuck a cookie and thinks you cannot tell? It is possible for you to have serenity by viewing him in this manner. It is amazing what they think you cannot see or tell.
Recently, I had a "BF" (he really was not my BF but he was trying to be and I let him try because I cared about him, he was like a member of my family growing up) who has been severely abusing drugs and alcohol for 30 years. He decided he was going to have an affair with his best friend's wife under the guise of helping them while the friend lay on his death
bed. For months he continued to call me, acting as though there was nothing
going on between them, while I TOLD him what he was doing. It was baffling to witness what he was doing to himself, and especially the fact that he could not see that I was onto his game.
I honestly believe that once they have progressed past a certain point, their brains just turn to mush. It is amazing though how they are still able to function in so many areas but just become so stupid in others.
If you can get yourself sufficiently emotionally detached, you will be ableto maintain your serenity to a larger degree.