Well to me Lena with Holly or Lena with Ian are what I call the believable / realistic relationships, or at least I think they fit that.
Anything else, specially from Slutty Lena and Holly paths seems to be here to fit specific fetishes: Corruption, NTR, Cheating, BBC... Which in itself isn't bad after all GGGB also had many different paths and if you are not interested you can just skip them.
There are a few instances where I don't agree with the way she's written a character, but I don't find it too annoying.