Hello,
Since the spots are non itchy and covering most of his trunk, the possibility of pityriasis rosea needs to be ruled out. Pityriasis rosea is a common human skin disease which presents as numerous patches of pink or red oval rash. Topical and oral steroids are needed. Water, sweat, and soap may cause irritation and should be avoided in the disease.
I suggest your boyfriend to get it examined from a dermatologist and get it evaluated.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.