I’ve liked my best friend for 3 years...?!!

Hadley
Basically, my best friend and I are seniors in high school. I’ve liked him since the beginning of sophomore year which is when we started to get SUPER close as friends. We’ve never been closer than we are now. No one can make me laugh harder than him. 
I’ve always wanted to go for it with him,  since he seems like he could be into it?? But he’s also naturally the flirty type without trying so it’s hard to tell if he likes me back and I’ve always had this nagging feeling he likes my other best friend, even though she says he’s basically her brother and would never go for it. He also isn’t the type to initiate a relationship or date someone if what he has is comfortable. 
However, prom is next Saturday and the people I’ve talked to about it are like just ask him as friends! Or ask him out! We’re going separate ways for College so we only have a possible four and a half months to be TOGETHER together. I don’t know if it’s worth ruining one of the best friendships I’ve ever had or I should just grow some fucking balls, ditch the anxiety, and go for it.
!!I’ll take any and all advice!!
(Also, if it says anything for how much I like him, I dated someone for two months last year and had to end it because liking this main guy in the background was too distracting and unfair for this other guy.)

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