Now, she has been my bff since as long as I can remember. But I think I like him. I would be very careful about this situation so that you don't hurt your friendship with you bff. Let their relationship take its path, whatever path it is, and try your best not to get involved. Don't let her know that you are interested in her boyfriend, and don't make it an issue between the two of you.
Friendship is much more important.
And since your bff is dating this guy right now, you should definitely back off, at least until they break up. At that point, if he does ask you out you can make the decision of whether or not to say yes based on how you think your friend will feel about it. I would definitely talk to her about it too, and see how she would feel if you and him started dating. If she is uncomfortable with that, then you might have to wait a little while before jumping into it. Dear Lucky, I've liked this guy since the 3rd grade.