Most of the time your party members will have consensual sex with either animals or other party members if you're not the one fucking them, an example would be the Succubus, Meredith and Tishtyra having a threesome. The CG probably doesn't change but the dialog and possibly some of the action does. Like with a corrupted Meredith, she becomes way more confident and dirty in sex whereas a pure Meredith is still the shy nervous spirit mage you met at the start of the game.
But for clarification, being the bad guy means more sex but it also means your party can get corrupted and in turn, you'll get sex scenes all of which are skippable.
Also, the walkthrough has a list for the sex scenes and the requirements for them. You can fuck not only your party members but also NPCs too.