Hm writing has never been my strong suit since I like numbers and DNA but....
I used to have something similar to that. This girl I met in sixth grade right after I had moved became my best friend. Everything we talked about quickly became an inside joke from things like pop tarts and fruit loops to how we would scream the word "Ahhhhhh!" It was just incredibly fun. Of course, I don't think we saw each other as anything more than just best friends, but that was before high school happened. I remember sitting at the table eating "beef nuggets.....what the hell" when she told me some person had asked her to prom. I was incredibly bitter but I didn't tell her I just laughed and asked her who it was then just teased her about it. On the contrary though, I was really sad and angry it was then I think I realized that I wanted to be something more than just friends, but like you I was afraid to take that extra step and loose what we had. It sounds incredibly cliche, but you really do find excuses not to take that extra step. "Things are fine the way they are or I should be happy with what I have, this person has supported me all these years what more do I want?" It was difficult for me though and as luck would have it her prom date ended up becoming her boyfriend. Eventually we grew apart, not that I really mind because things like that happen when everyone gets a significant other for the first time, but arbitrarily one day she called me and told me she had broken up with her boyfriend. After a few months, I finally did it. I asked her out. It turns out we were both jealous of each other's prom date and were both hesitating. We wanted the same thing yet at the same time thought we should be content with where we were.
Now that we're in college, it's been a few years. Not all things have a happy ending like dramas and we ended up having a mutual break up. We still talk to each other but not as often and it doesn't feel the same as it was before so obviously something has been lost during that transition (though I'm sure there are some people who can pull it off and go straight back to what it used to be.) I must say though, I don't regret it at all. It sucks that it didn't quite work out, but it could have been a lot worse. I think it's better to take that risk and see where it gets you but then again though your circumstances are different.
Wow I wrote a lot even though I hate writing. Stealing your journal oh ho ho ho ;3