Who says? What authority, other than your opinion, do you rely on to assert murder being far worse than adultery? Because our law and courts gutlessly treat adultery like no wrong at all?
Murder ends a life, adultery does not. Murder takes a person off this planet, can take a parent from a child or a child from a parent. Murder can kill the unborn. Marriages and families can survive adultery, but not murder.
I never treated adultery as no wrong at all. Yours was a terrible assumption.
I never cited an authority, and need not have. I gave my opinion, which, I will add, is quite logical, even in a spiritual sense.