I'm a wreck..seems like i never get the girl i want. give me helpful advice?

I like this girl, 3-4 inches taller than me, and we're friends, high school seniors, but it looks like she always looks at this friend of mine who is two inches taller than me and he always seems to stand out. I try to stand out too but he shines academically and i can't do anything. It feels like i'm being the one who is always used and pushed away. I had a relationship during last summer with a girl i liked on the surface and i stopped dating her when i couldn't handle how she questioned our relationship every date and THEN, i find out that she's been on and off with this other guy WHILE dating me and they became an official couple shortly after we broke up. The previous crush i had ended up crushing me VERY HARSHLY. (my heart was in pain, i hated her alot because i felt betrayed and used) And the crush before that ended like this : Her brother finds out that i like her and bullies me around, forcing me to go to her every day after school and embaringly yell "i love you" out loud. I've suffered so much love trauma. I've pushed away possibly the only girl who liked me and now i'm just pathetic and feeling like crap. I suffered a chickpox attack last year so my image was ruined. It seems like nothing good happens to my love life.