Well, the game kind of tries to eat the cake and keeps it too in this scenario. Depending on the variables both Ian and Lena will say that they don't feel ready for a relationship and want to keep it casual. But they also talk, regardless of love flags, that they feel "something special". But they still leave it completely free to fuck around with any and all other guys and girls, so that really whole "something special" seems like just some cheap lip service than anything real.
The thing is, ultimately it comes far more to "show, not tell" and what the player has both Lena and Ian actually do in their playthrough. And some of these actions really stretch the plausibility of "and then they became a pure-loving throuple with eyes for no one but only one another".
Or, to put it differently, apparently the simplest way to get the "Holly Trinity" is for Ian to avoid getting in relationship with either Holly or Lena, and for Lena to hit on Holly (in-between fucking whoever she pleases) Which i find really hard to believe was EK's intention regarding this relationship, when the alternative paths require you to jump through all sorts of hoops.
