have you asked him if he's had other partners recently?
grace
So if this is a non STD dermatitis why would you think that he cheated?
Nonsexual: These causes of NGU may include: urinary tract infections, an inflamed prostate gland due to bacteria (bacterial prostatitis), a narrowing or closing of the tube in the penis (urethral stricture), a tightening of the foreskin so that it cannot be pulled back from the head of the penis (phimosa), the result of a process such as inserting a tube into the penis (catheterization),