How can I keep my confidence up?

Well, my life is going great… I spoke to my crush, found out something about my crush which can make us a liccle bit closer, got into a new sport and having the best time ever with my friends, having a great week and just upped my confidencee loads.. . But the thing is im only high in confidence when im with my friends because I cant bear people talking about me, and it blows my confidence if they do. Im not in there lessons or anything so I have only a lil bit of confidence in classes, im like the quietist when theyre not there and all my teachers say I need it boosted or it could lower grades in speaking tests etc.. Also alll that stuff that happened could go because I wont be able to talk to my crush because ill be too shy, wont carry on with new sport because to shy.

I love my confidence when its high because I feel to happy to care what anyone thinks, but my confidence goes so easily! How can I keep it up without having my bffs there basically holding my hand helping me all the time! I wanna show them I can do it myselff..

Basically how can I keep my confidence up?