How do you handle the girl you're crazy about having a crush on another? We're best-friends, and she's honestly my everything. I don't think I could handle being rejected or seeing her with another

Try to be supportive. She is your friend and she deserves to be happy just as much as you, If it makes you very uncomfortable try talking to her calmly and asking her if she really likes the other person. She will probably end up getting over her crush and if she doesn’t I’m sure there will be someone better for you.

In my opinion I think that the most important thing is to talk to her about it, she’s your bestfriend and I doubt she’s gifted with telepathy to know your thoughts— vise versa. You need to tell her your exact feelings and only then the both of you could move past the problem and do atleast something about it. I know it may feel difficult because i’ve been in your shoes and i’ve felt that feeling of hopelessness, but no matter the outcome you should always be honest with her, because if she knows then she can atleast consider your feelings.