It most definitely intersects with the Nikki path.
Nikki might not have any personal feelings towards Julia... But she does the math and figures out you've fucked Julia during the middle of your relationship.
Needless to say she doesn't appreciate it
For the girls from Madison Springs it doesn't matter, it was before you ever met/reconnected with them.
If the MC never learns of it... this could be happening in every game with every LI

, technically.
NewGuy2022 probably has the correct definition on a dictionary level.
Personally i wouldn't have a problem if girls i passed on started dating new guys(hopefully not Ethan or Zach), that's just how life works...
But... amongst AVN fans you'll always find some who are deeply offended by this, so it kinda becomes more trouble than it's worth.