The first problem is that Louise always makes a move on Ian, regardless if he or she is in a relationship. She can still be with Jeremy and Ian can date several girls, including her own roommate. Weirdly enough, she only doesn't post if Ian dates Holly. I don't see a plausible in-game reason, its likely that Eva doesn't want Ian cheating on Holly (its currently impossible IIRC, he would break up with her if he is dating others on the side), so every girl is removed clumsily.
Her profile text states that she is a loyal friend. She also shows this by wanting serious relationships with her partners (Jeremy, Lena) and demands commitment, she is immediatly jealous and insecure if they don't do that. So her making a move on her roommates boyfriend is flat out out of character. You may argue that she could be angry with Lena, which can be true on some routes, but not all.
The second issue is Ians inconsistent behaviour. At first he is extremely smug and dismissive about it, toying with her, regardless of his behaviour throughout the game, regardless if you didn't make him a chad asshole. It can be very uncharacteristic. Then suddenly, just after multiple texting, he feels to be in love with her, is all romantic with her and may consider her as his anchor if he breaks up with Lena. Its very rushed, Ian and Louise barely interacted within 12 chapters and seems to be written on the spot, with no proper foreshadowing, backstory or previously development (Louise can like the threesome, I guess that could count, its entirely optional though).
Wouldn't be surprised if throwing in Arthur and Lena magically wanting to flirt with him to start a new route this late in the game was a similar take.
