My Husband Is Slee Ping With My Mother, He Says My Mom Is Sweeter; PLS I NEED YOUR ADVICE!

My mother is an attractive and interesting woman who dresses fashionably. Recently, I found out that my 39-year-old husband has been having se x with her when he attends conferences at the resort near where she lives. When he told me, I was bothered by the fact that it didn’t bother me. He’s a wonderful man—father to our two children and a good provider—and he’s always taken care of me emotionally, se xually, and financially. I know I should be upset; I know I should feel betrayed on so many levels. But I just don’t. He says he enjoys the relationship with her but will stop if it’s what I want. Honestly, if my mother and husband are happy in their affair, I just can’t seem to find the energy to be angry or jealous. So my question is: Is this normal? Should I be upset?