Is it still posible to play the entire game NTR free, and still have a harem
You can disable NTR right at the beginning of the game. It prevents anyone fucking the girls other than the MC.
BUT: The MC is one who takes other men's wives for himself. For example, there is a farm girl helping you right at the beginning of the game who has a husband that isn't home, because he's participating in war.
You can take said farm girl for yourself, but her husband will come home and you can then get rid of the husband without the girl getting back together with him.
In most cases the other men are mostly scumbags, so it shouldn't bother you much from a moral viewpoint. But just to say it, before you start playing, these are part of the story and the world building so they are unskippable.
And yes, the game will naturally lead to a harem-like setting.