How i get that track skill?
The skill is one of the first you can get, they cost 1 skill point. At the beginning you can buy it.
For the guide for the ending with no NTR. I will try give some pointers here.
Get the skill to know where she is and when an event is happening. You will know because you will see a heart where something is going on.
The first days you will see the other guys interacting with her, you can't stop some events from happening.
Try to get the stats the game asks for each exam, and get some extra points because you get money when getting a good rank in the exam, 10k gold when getting 1rd place. It will help you a lot.
Also, get the skill so your lockpicks don't break, at the beginning you will struggle with money.
To make things a little easier. You can get the hypnosis book from the library and you wont have to deal with the teacher. It isn't sure, but I believe that when you are doing good in the exams you don't deal with the kid.
Try to get stamina fast, and buy some potions from time to time from the store.
When needing money, work at night, it gives you a little extra.
And more importantly, save often. Even if the guys get something like a kiss, you can always stop them before she gets fucked, but when they get a scene, you won't be able to stop that scene later. Also, the more you stop them, the less chance they try again.
Any other question, feel free to ask.