This is gonna sound condescending but if you're still seriously thinking in terms of "best friend" then you might not have the life experience that would show this.
As a teenager every time you're close to someone you're attracted to, it feels like a potential chance for sex. This manic energy is going to ruin a lot of things. This manic energy also does not last your entire life.
I have a lot of very close friends, and we get enjoyment out of hanging out. One lady in particular comes to mind, because if I was a teenager I'd probably be trying to get into her pants. I like sharing jokes with one friend over IM cause she's funny. But she's also a little mean and I wouldn't want to tell her some of my insecurities cause I don't think she'd be nice about it. I can't imagine waking up and seeing her in my bed. It's an uncomfortable idea. Imagining fucking her is fun, but seriously if the chance came up, I wouldn't have sex with her. But I enjoy her company a lot and I want to impress her and I like hearing her thoughts.
Relationships are as unique as the people in them. There's gonna be good and bad with each person you meet. Getting on the level when you're cool with being emotionally and physically open with a person, while they find you attractive, while you find them attractive, is actually a pretty rare combination. It's not a problem that's gonna come up very often.