How do you get the good ending?
After the "Terena's nipple pull prank"/EV09, the girls and Kurt go seperated ways for different reasons.
Arika and Rietta went to the castle library to find ways to counter plant monster (especially aphrodisiac one, like the one from EV02), and Terena confronts the brat for the nipple prank from last event (EV09), and Kurt went to the guild... For reasons I don't remember (it's been a while for me).
When is about to leave the guild, you will be warned that your next choice as you leave the guild, will affect the story.
A good place to save, just in case.
When you are outside, Kurt will be worried about the girls, and start thinking what he should do.
The game gives you 3 choices, but in reality, it's only two paths from here.
Chosing one of the two above, will continue the story's NTR path, and the girls will caught in traps that will doom them in a path of pleasure.
Chosing the 3rd option, Kurt will head towards the girls and save them from the men, and you are basically heading for the good/harem ending (or as much of an ending as it is, at this point).