Haven't touched the game in months so I'm a bit rusty on the game knowledge. One of the key things to do to get the NTR started is setting parameters for the heroines and the visitor in the settings. If I remember correctly, it is possible to set the favor and NTR stats such that they increase faster. You should also make sure the visitor is hyper-fixated on the girl you're going out with such that at the start of every morning, he beelines it straight to her location every time. After, that he'll usually start off talking and eventually they'll start doing other things. This process can be sped up or altered by giving the heroine traits like (likes NTR) and (cheating) but by doing so, stuff can get really confusing really quickly. I just experimented with the game over a long period of time. In hindsight, I'm not really sure why I recommended the game. I really like it and see the vision but its honestly a pain in the ass to figure out. If you've got the time and curiosity then just keep on fucking around with the settings til something happens. If not, then I advise just moving on to something else to save your time and sanity.