To clarify
Modsarenotvirgins' reply, the NTR path is largely dependent on how well you take care of the LI's, and has almost nothing to do with where else you happen to be schlicking you schtick. The MC can be as morally corrupt as you would like as long as you don't make choices that negatively affect the LI's, and you'll avoid the NTR content. At no point (after far more playthroughs than I care to admit) have I encountered a situation where the LI's "lose interest" in the MC (possibly on account of his egregiously enormous erections [I apparently alliterate after a few drinks]).
I would say that the "extra" amount of NTR content is purely due to having more participating characters in those scenarios. The primary story, itself, doesn't diverge dependent on whether or not Matt (fuck Matt) bangs your sister. There is still a linear core to the story. As the game so far does not (and hopefully almost never will) have an "ending," I would say that the NTR/Loyalty paths are fairly equal, and largely play more of a role in the individual players' satisfaction with the sequence of events and who puts whose oversized Tab A into whose shockingly tight Slot B.