Just wait for few updates, and you will see jeremy breaking that rules soon. Particularly with Lena. No matter if it is lena who will thrive for jeremy, Jeremy co operating it would be ultimate betrayal for Ian and also his own self's broken principle.
As far as I remember, if Lena has sex with Jeremy before Ian asks her to meet, she refuses him, just because of sex with his friend. And if, uh, she's slutty enough the moment Ian asks her out, you sort of start an experimental relationship that just involves sex outside of a relationship. So, something that you say cannot come true. And if you have a normal relationship, she will not sleep with Jeremy, you will not be given such a choice, or rather he will be gray.
In fact, it is YOU who choose what boundaries Jeremy can overcome. YOU are the builder of this world and it is YOU that is the very thread, it may seem to you that you are playing for Jan or Lena, and this is partly true, but YOU are the thread, the very thread of fate. In our reality, you just sit at the computer and poke at the options, but in the reality of the game, YOU destroy lives, create pairs, YOU are the inevitability itself, YOU are fate. And it is up to you to decide how the lives of these puppets will develop.)))