Honestly one thing that strikes me as being particularly characteristic about Fuuko is how she would manipulate any situation to get closer to Yuni. Like how in chapter 2 she had deliberately brought her close to the area surrounding love hotels, and also at night mind you. At this point it shouldn't come as a surprise that the kind of guys showing up later would happen. From there Fuuko can actually get closer to Yuni by helping her to get away from those guys, which tugs at her heart strings.
Yuni for the most part has been rather infuriating as of now since she just posts all her stuff on the internet with her face on it. Like mate, a half obscured face can easily be recognized by anyone who knows, much less someone who seems to be stalking you -.-.
Also considering how she just continues to shit on every little problem that goes on between her and Nanase just shows of how there is so much tension between them in their relationship. Not to mention that she isn't willing to take steps herself to strengthen their relationship, but instead waits for Nanase to do it for her. At this point I wouldn't surprise about Yuni just doing it with Fuuko out of pure jealousy (wherever that may come from) and when Nanase confronts her about it, would just blame her for all these things that she shows less than enthusiastic response to. But I guess the kind of person who would be her ideal partner would then be Fuuko since she would be able to even the slightest things about her, being her stalker and all.
Of course, Nanase herself too would be at fault, having never clarified many things with Yuni such as her reason for being secretive about their relationship. I mean it is kinda late to wait until your girlfriend is about to break up with you to start revealing the rationale for it. And if after her confession this doesn't lead to her taking progressive steps for the sake of the relationship, then it's shouldn't be a surprise about what is going to happen.
Though I can honestly see how the drama would unfold from a mile away, I'm still hoping that Yuni and Nanase can both put in the effort to solidify their relationship instead of leaving it as volatile as it is right now. Though I have a bad feeling that Fuuko isn't just gonna be an obstacle for the two girls, and this story isn't about their relationship recovering...