I was thinking this too. Was it that they had smaller interpersonal space but otherwise a genuinely platonic friendship that tipped her off or were Jake and Lena deliberately dropping hints or even trying to mark OP as their territory? I was originally thinking the former but if they are now going on about him choosing some girl over them, I wonder if they deliberately or accidentally in purpose sabotaged things to get their triad back.

What confused me about that is, had she brought something up before about weird behaviours or is this the first time? Had sexual history ever been a discussion between these two? Past partners etc?

I may be overthinking it, but I've always been someone who has these discussions early and found that it works out well for me.

While I was reading thought Sabrina would join the trio but since it’s a tifu post I remembered there won’t be a happy ending ( no pun intended)