Could anyone please tell me where and which choices should I make to avoid NTR or sharing route and still succeed with enough points?
Only real NTR is in week 3, where it is an easy decision (you get to pick between two objects, one is labeled LC, one NTR), at which point the "points to continue" question has practically ended.
As for sharing, there are also obvious decisions on whether or not you want to engage in that, however, at least one LI will have sex with another guy (her boyfriend) without anything you can do about it except for completely avoiding her route. Another girl is a cam girl. And with the whole setup, "sharing" is commonly talked about (though I wouldn't call it "sharing", since this is for the most part a "young people fucking around with everything that moves" game, and even though you can get romantical endings with most of the girls, for the most part they are just fuck buddies/friends with benefits).