Not necessarily. Some might just want Lena to be a slut with chads Ian and Jeremy filling Lena's holes in a devil's threesome (which Lena can fantasize about). These complex decisions can't really be interpreted in one obvious way. I can also present a counter-point that uses the same logic as yours (supported by canon): If you want to commit and be together with Ian in a serious relationship (let's remember that both Ian and Lena have issues with cheating partners), you shouldn't have slept with Jeremy a.k.a. Ian's friend who is known to have a code for not sleeping with bros' girlfriends. There's a clear writing on the wall that this choice has negative consequences for Ian x Lena just like there is for Ian pursuing Cindy or Lena fucking Axel or agreeing to be Seymour's toy.
And like someone said, that's also assuming you're playing this game on your own, instead of playing it with your gf who has a completely separate playstyle and agency from yours, and you, playing as Ian, might not have wanted for Ian to turn into Eric because of your gf's decisions. And while that's not the designed way to play the game, I think the game should still treat Ian's and Lena's agency separately and not assume that the player has one grand plan for both.
Even if you're playing by yourself, the ability to roleplay as Ian and Lena differently creates amazing opportunities to direct an interesting story. So I think it's fine when the choices you make for one protagonist, can then result in a consequence that deprives you of agency for the same protagonist later (like Ian falling in love with Lena not being able to commit to Alison or Holly). But it's not really immersive if making a choice for one of the protagonist, removes agency for another. Which is why I think Ian-Holly-Lena drama was so controversial, because players wanted to roleplay as Ian and Lena in their own way, but worst of all, it was NPC's decision (Holly's aka Eva's) that deprived both Ian and Lena from agency to handle that situation in a mature way.
That would be the ideal solution, but also creates a LOT of additional work (as I already mentioned, it would ruin friendship with Jeremy and block Alison / Emma sharing routes or make them toxic, with Jeremy fucking them anyway on the side), and not at all ideal for Eva's gardener style of writing and requires planning a lot of chapters ahead to start fleshing out the route as early as possible. Maybe once Eva has fewer branches to worry about, there might be another smaller revision down the line / DLC that would include that branch, but for now it's important for Eva to stay focused on already established routes and not lose track of them (which requires yours truly to untangle the mess of variables and keep track of all the branches). So if Eva excluded that path for now, it's for clear reasons and is part of the planning to continue releasing the chapters in 3 month window.
Yes, of course, but that requires time to revise everything so you'll have to be patient.
Nobody promised that he'll turn into a completely different character in the revision, but every single interaction with him has been reworked and expanded upon.