You must have learned how Samarra adopted Nell (it's the very last "talk about samarra" dialogue with Samarra). Once you've learned that, then guessing the correct interpretation of the Fairy Queen's vision (spawn rather than seed) leads to her giving you a quest involving Nell.
To have all the clues you need, you must have gotten all of the crone's training, and also:
There are a couple day by day, action by action walkthroughs available if you google. They are useful for figuring out the puzzles but very bad for getting unstuck.
so get 1/8th of the content if you want a good end congrats
The "sad ends" he's talking about are only if you knock them up and don't choose them in the end. That's a very intentional thing (you have to deliberately remove the contraceptive spell AND cum inside them AND not pick them in the end) so you really only have yourself to blame in that case. Other than that though, you're free to romance everyone (though you still have to pick one in the end), so I don't know where you're getting this "1/8th of the content" from.
How is that "1/8th of the content"? You get the whole content, you can get all non pregnant endings from the same save even.
I think the "sad" part meant is how you get an epilogue where you get details (depending on the character) on how heartbroken the girls are if you did not choose them. Primrose is more or less completely lost and throws herself into the library work, Callie occasionally finds "love" but also is unhappy. Nell and Evelyn also seem affected, though less than the others. The rest seems to be relatively fine in the long run though.
Man go out side and touch some grass please.
There's NTR in the sense that the MC steals another character's wife.
Sand pit near the town hall. You have to learn about it from Nell first, though.
