The pain/anger from getting cheated on as a man comes from years of evolution. We have a natural urge to pass down OUR own genes. Back on the African plains, we didnt have paternity tests, abortions, or child support so it was a pretty safe bet that if you caught your cave woman fucking another cave man that she probably conceived his baby. And shit is rough in Africa. So now, you gotta survive wild animals, starvation, disease, etc., and hunt to support a child that isnt even yours. Thats crazy. But truth is he probably would just kill her and the partner. Idk, Im not a scientist or adjl.
Now on the other hand women feel pain when cheated on as well. Just like men do. But theyre more apt to forgiving cheating because in a way it just further validates who theyve chosen for a mate. Hes a stud with options.