So the ntr is optional then? And I can just choose the alpha route? Also how exactly do you choose a route? Am I gonna be given a chance to choose at the beginning of the game about which route I want to pursue like in Parental Love or it's completely up to me to figure out which of the dialogue choices corresponds to the route I'm going for?
Yes, NTR is optional. You do not choose at the beginning and you are able to jump paths at certain points during the game. It is even possible to be locked into paths if you do the "right/wrong" choices. e.g. There is a choice with your Mom, if you choose the "wrong" one, you will never get her exclusively therafter, only wife-sharing or happy voyeur at best, beta most often.
On the other hand, there are choices which let you "man up" getting away from the beta paths, if you were on them.
Confidence points govern how alpha or beta your character is. Many events depend on your level how they work out.
To pursue your Mom and/or Sis, you need corruption, love points and high Confidence. For other girls the corruption points are less important. If you go towards an alpha "wife-sharing" Stag path, you will need some slut points as well.(Even on full Alpha it can be positive to gain some slut points if you gain other points with them. As long as you keep decent love and corruption points, the slut points do not matter too much - or you want to go towards a wife-sharing alpha)
The Happy Voyeur needs lots of corruption, love and slut points and a halfway decent Confidence score.(What can be hard to keep up. It needs some thought to hoard enough confidence points, do not go too far into the negative)
The total beta has high slut and corruption, bottomed out confidence and love. One reason the happy beta is so hard, is keeping love up and esp. a couple of Confidence points. (So while you might be deep in the red, you are not totally down)
Finetuning is the key on the diplomat routes. Depending which girls you pursue, this can be rather easy (e.g. just going after Mom and Karla) or really hard if you need e.g. lots of opposing points.