Maaaan, I am going to take the unpopular opinion and say I wanted Chihiro and Aoi together. Chihiro definitely played her whole relationship wrong and was a bit manipulative but I don't doubt she truly loved Aoi. Mostly though, it's because I am stubborn and always root for the "first love." Also because I can never understand the whole falling in love with somebody new, while you already love someone, because they "listen" or "are there" for you. Seems like any sorta nice friend can fill that position, but not Chihiro haha, and somehow it overules the love that was formed through years of friendship
Just because one loves someone, doesn't mean they are the right person. If love was the only thing that mattered, we'd be having a lot less relationship problems in the world. Having someone "listen" and "are there" for you, to me, is one of the most important things in the relationship. It means they respect you. Sure any "nice friend" can fill that position, but in my opinion, that's not really any different from the childhood friendship. Just because you're a friend that is there for them doesn't necessarily mean they'll fall in love. Just because they're childhood friends doesn't necessarily mean they'll fall in love.
From what I saw, Chihiro never respected Aoi. Loved her? Yes, but I never saw her respect her as an equal. Like what kind of sane person would purposely drag around someone that loved them and loved them in return, just for fun? Just because it's cute?
Nao was also pretty manipulative, swooping in and taking advantage of Aoi's emotions, but she respected Aoi's feelings and was willing to sacrifice her feelings to let Aoi go after Chihiro. Chihiro on the other hand, hid Nao's feelings from Aoi once she found out the truth and thought of this as a way to get Aoi back in her favor. She's just constantly playing with her. In the end, Chihiro wasn't even upfront to Nao about Aoi's feelings and Nao had to go fight for her love herself.
When you compare them side by side, I'm sorry, but childhood friends or not, I would never want to date Chihiro. I'd take a new friend who "is there" for me anytime over a childhood friend who's been constantly playing with me.