Psychoanalyzing fictional characters is always a bit silly, but I think the term that best describes Yuu's behavior is demi-sexual. Demi-sexuals are people who only develop a sexual attraction to others after they have formed a strong emotional connection with that person.
We've already debated this in an earlier post. We have no idea what Yuu's sexual attraction is like, we only know about her romantic attraction. If you argue Yuu developed a romantic attraction to Touko after a long time getting to know her, then you could say she's demi-romantic. But Maki-san has stated right at the beginning of the story (chapter 7 I think) that Yuu was also in love with Touko, even back then. So it's not like she and Touko were just friends and she slowly began to develop romantic feelings for her, those feelings were always there, they just grew stronger and more evident with time.
Also, thanks everyone for using the spoiler tags. I really don't want to read spoilers to this next chapter.
You are correct in that the term I probably should have used was demi-romantic. However, it is made quite clear in the story that Yuu does not begin to develop romantic feelings towards Touko for quite some time into their relationship and chapter 7 is actually a good one for making this case and point.
To begin with Maki is just an outside observer. Basically the driving narrative in chapter 7 is Maki's misinterpretation of Touko's public display of affection leading him to confront Yuu about the type of relationship he perceives they are having. Maki asserts that he thinks they are a couple and are dating and Yuu tries to correct his misunderstanding.
Maki states that the affection in their relationship seems to be quite ones sided, but then notes that Yuu must really love Touko because she worries about her welfare before her own. Yuu however is puzzled that Maki would believe this equates to love because this is just generally how Yuu treats other people. It's one of her defining character traits and flaws. She tends to always put the feelings of others before her own.
At this point in the story we are a month into their relationship which is not a trivial amount of time and Yuu herself still does not believe she is in love with Touko and argues such with Maki. It is however noteworthy that this is really the first time in the story that Yuu does begin to question what her feelings towards Touko really are and she begins to wonder if there is something more to it.