Holly might try to break Ian/Lena relationship on her slutty path. Just like Lena took Ian from her grasp when she was meek. Probably a power move by slutty Holly to feel desired and out of spite against Lena. The word ally is used in the beginning of the game to describe Holly's relationship with Ian and Lena, I smell a backstabbing coming soon from slutty Holly or maybe I am reading into it too much.
Was the Ian that ended up with Lena, ever really interested in Holly that way? He was interested in her as a fellow writer, and may have admired her, and just wanted to be around someone who was already successful, but did he ever really see her, the way he saw Lena? I don't think so. So I don't agree that Lena took him from Holly's grasp. Because the first person he meets in this game is Lena, and if Ian is on her relationship path, from that moment he's totally enraptured by her. And Holly never really gets a look-in, unless you allow it to happen.
Of course, Ian can innocently give Holly the wrong impression of his intentions. Because even now in Chapter 12, he was quite surprised to learn that Holly fancied him, or at least she once did. And I suspect slutty Holly is secretly somewhat aggrieved by this, and might have decided that stealing Lena away from Ian, will be the perfect revenge. Probably, because that is what Ivy would do, if faced with a similar situation. Everyone, needs to stop thinking about slutty Holly, as the sweet innocent she used to be. She's now being molded/corrupted by Ivy, to be just like her. And Holly jumping straight into bed with Robert, a total stranger, demonstrates just how successful Ivy's attempts have been, and just how willing now Holly is, to go along with her ideas.
I just wonder whether a really slutty Holly, will eventually get enrolled on Ian's cuck path, with her and Lena having sex, and forcing Ian to watch. And when Lena taunts Ian about cheating with Axel, Mike, Marcel or Jack, Holly joins in and reveals her sexual experiences with Robert, something he personally will never have with her.