You aren't a guy best friend to her anymore though. You're a guy who is interested in her romantically who is creepily hiding his feelings so that he can be around her. Relationships are built on honestly. Tell her your feelings and get accepted and rejected and deal with that. Maybe you'll lose a friend, but you'll be free to find other prospective girlfriends or friends on whom you do not have a crush. It is more likely that she'll say something like, "Let's just be friends" and you won't lose anything, but then you won't be a creep anymore and you'll know that your feelings aren't returned so that you can move on instead of hoping.

Don't give advice on relationships and guy crushes if you're interested in someone. You have to know that is incredibly creepy, right?