I think it's an after dark cinemax movie made between 1988 and 1991. Where a girl dj is murdered while she on the air I think. I believe a guy who is a good friend and a detective starts looking for the murderer and he gets help from friends of the girl that are possible suspects that he ends up sleeping with. One scene has him having sex with a girl in the bathroom at a club or restaurant. He also calls or visits two girls that he knows for information. They give him some info and then when they are done they are about to have sex and I think they ask him to join but he doesn't so the two girls have sex with each other. I'm going off memory from 20 years ago so sorry that the details aren't better.