As someone who was in the same position just recently, I can really appreciate this oneshot.
The title of bestfriend should not be taken lightly. As a bestfriend, you have to be able to have the mental & emotional fortitude to support your bestfriend through thick and thin. Unfortunately, like Rina here, I also fell in love with my bestfriend who didn't think of me anything more than just a bestfriend. Having unrequited feelings for your bestfriend is very different from having unrequited feelings for others. There will be tendencies when one or even both parties might feel betrayed.
I actually think the ending was beautiful, coz it seemed that they will continue being friends after that. When I confessed, she blatantly rejected me and told me she felt betrayed, and we went from bfs, to friends, to not even being friends in facebook. lol.
Even though falling in love with your bestfriend is pretty hard to avoid, I think sucking it up and still being with them even though the feeling isn't mutual is much more harder. Not all of us are as strong as Tamao-chan from Strawberry Panic, who, not only was able to push Nagisa to be with whom she loves, but also was able to accept Nagisa back into her life. I always revered Tamao-chan for being the shinning example of what a bestfriend should be when it comes to falling in love with them.
Anyway. sorry for the long rant, but this read really opened up some past wounds. xD