My fiancé gets a red rash on inner thighs & groin after intercourse. It looks like pictures I've seen of jock itch. What could this be? I have no stds

Best to have exam. It would be best to have the rash seen by DERM or your DR. Then a accurate DX will be make, sometimes scraping of the rash will be needed to confirm DX, and this can only be done after an exam. Best to get an answer now, rather than worry about it for the future.
RASH ON THIGHS/GROIN. THIS IS PROBABLY A REACTION FROM EXCESS SWEATING AND RUBBING. DOES NOT SOUND SERIOUS OR CONTAGIOUS.