How can you be confident without being good at something?

FYI I'm in high school and It's just I've had a constant problem socially that goes all the way back to when I was 8 years old and I guess I'm just very insecure, but I have had a rollercoaster ride in my social life because in Elementary I was a loud, confident, outgoing, and had many friends. But when I went into Middle School I was a pretty big nerd because I wore gles, was bony, played lots of video games, and I wasn't very athletic. So I got picked on for it and I became very angry and unconfident only engaging a real conversation with people more unpopular than me...so I guess the problem is I don't really feel confident unless I am the most dominant or close to it. But then I got into sports (mainly soccer) and became slightly more athletic and the kids I played against kids who were so lazy or uncoordinated, so they made me very confident and then I just got y, when I really wasn't that good. Then I made too high ambissions like being the captain of the team and I didn't even make it and I actually didn't work for it either because I thought I was already good enough, so that was definitely a real blow to my self-esteem. So I am just barely better than average in my athletic abilities. And so that has boosted my popularity to middle-cl and I just still feel miserable, but I am happy I have friends that I can have normal functional relationships with. But I am very envious of some of my friends because they have a gf or have gotten laid and they ask me why I haven't done either yet, so I made up a story that I had a gf in middle school (since not many ppl knew I existed then anyways) and said it didn't work out and most ppl bought. So since not making the soccer team I have had many rejection issues and insecurities. I also feel uncomfortable speaking in front of a cl, but I manage with that. But since then I have made the soccer team for the new high school I go to (only cause there's not that many ppl attending) and I don't even play that much and ride the bench most of the game. Socially ppl just see me as jus some kid who was in that one cl or I guess an average joe. But I also see ppl who are bigger losers than me getting decent gf's and I just don't get it. Anyways sorry for writing a lot, but I want to know how to be confident without being good or just average at something?