How could I be so stupid?

How could I have been so stupid?  How could I have been such a coward? Somehow I didn't have any courage whatsoever. Me the big guy. Didn't have enough courage to ask a girl the simple question of "Do you want to go to prom with me?" Now she is dating the guy who she ended up going with and I am stuck on the sidelines trying to hide my feelings and not show her how hurt I am. I feel like an idiot for not having the courage to ask that simple question. It could be me that she is still talking about, It could be me that she is dating now. But  of course I didn't ask and I have to deal with all this regret. How could I be so stupid?