Firstly, never think it is about you. Does this other boy know that you were interested. Maybe he thought you werent interested and your friend expressed or showed him she liked him and showed him she was interested. If its meant to be its meant to be.
Secondly, these inner thoughts are your own about not being good enough. What i mean is that no one can see or hearcthem but you. I bet you you are the only person that believes this. I bet you have so many amazing friends that would think and tell you otherwise. If you believe in yourself, you should by the way! Then this internal thought will be externalised. Start small, one step at a time, think of everything yyou have and achieved, recognise that you deserve to be proud of your achievements and stop being hard on yourself. As i know myself, we are our own worse critics. If that fails, if a friend came to you seeking advice, saying they wrent good enough, wouldnt you stop that nonsense talk. Look at it from another point of view, in someone elses shoes.
I do hope you realise that you are good enough, andcut will take time and practice to get there. But never give up. Please dont be hard on yourself, i know that no one else thinks this way of you and any true friend will help you realise that. Hope my words help you to see things in a different light! All the best!