There are a lot of good games already mentioned, but there's one game I haven't seen anyone talk about that I really liked, which unfortunately only got a few updates before being abandoned, called "Beginnings" by Zyzonia. Even if the game is pretty short, it has a great sex scene that plays differently depending on your choices, and there's also another pretty good sex scene you can get just before the game ends.
It had so much potential but it did seem a bit too ambitious with the different paths, selectable camera angles for the animations, etc.