The number of side girls that are confirmed prostitutes: Quinn, Riona, Camila, Sarah, Melanie, Mona, Lily, Nicole, Sandy, Rose, Madame Rose.
From the remaining LI's and side girls, most are cheaters (Josy, Maya, Sage, Jade, Cathy, Tara, Kylie, Heather).
The only girls whom are not (yet) confirmed prostitutes or cheaters are: Jill, Bella*, Zoey, Becky, and Nora. (assuming the latter two don't have confirmed relationships)
On the one hand, it's impressive how many different girls have lewd scenes in this game. On the other, if you draw the line at prostitution and cheating, then it's a very short list of girls to consider! Of course, DPC is a huge DIK, so MC is liable to get an STD only from those latter girls (glances at Becky ...).
Also, it's kind of weird how many girls have lewd scenes in public restrooms (YUCK): Riona, Camila, Sarah, Tara, Kylie, Mona, Nora, Josy, ...