Please help.junior in high school. lack of friends. dont know where to turn to anymore?

i am a high school student in the 11th grade.... i lost many friends slowly since the 5th grade.... i have some friends who i speak to online and maybe i speak to 5 of them in school but usually barely hang out maybe once in 3 months... and i also have this one "friend" who i suppovely bumped into this spring break in florida, and we chilled and went to a movie together for two nights in a row. now when we get back to new york its like he doesnt even know me, but usually i instant message him on aim . So i have a friend problem,and i really dont want to switch schools because high school is almost over.. I really wnat to change and show people that i am a good person, but in my school there are two types of groups and i feel like i will never get into them, and never wil i used to be friends with the people that were in it.. but not anymore.. they look at me in a different wayl. On facebook there are pictures that my so to speak "friends" have and they are with everyone in our school and i look and i am really jealous how i am not invited to any of these gathers which is usually every saturday, and then i feel like crying.. i barely go out on saturday nights to clubs or anything because im not invited... I really dont even like going into school groups or sports because it takes up too much time after school and then i cant concentrate on my studies and i am not doing so well in one of my main subjects. I serouisly am sick of life and I sit home on saturdays and my parents always ask me why i dont go out with my "friends" and i ask my friends to go out some saturadys but they usually have an excuse. please help me, im not a nerd im an average good-looking kid in high school and when i look also at people or my "friends" i roll my eyes because they think they are better and better which [they are]. please help me how can i fix this, i really cant anymore with this without have friends. If i try to attempt to talk to people. they make like faces and likee act like "wtf is he doing here" Nobdoy is welcoming in my school. EVERY grirl is prude too. and the guys are also like the girls and dont talk to anyone that isnt in there group.