Info is important, details are not.
Whoever is out of the loop deserves to know if he is sleeping with someone, who is sleeping with others. He reserves the right to plan/protect his own health.
Flip-side : Shouldn`t YOU know if either of them have other sexual partners ?
As for details,...not needed, not owed. For the 'stage' you are at in dating, I`d say anyone demanding details, is looking to control the situation.