Can somone please tell me what wrong with me!??!?!?

ok i have this girl friend and its like every time i here her go with a friend to a party or something i get all worried that she might go out with him or even if its a girl i get al woried cuz i kinda have no life and she does and i just get so sad when she goes to placis and i dont.........when shes happy im sad but when im sad and she fells sorry for me i get happy ( its like i really want atention from her) its so weried.....and its like if she dosent give me atention and talks about her best friend i wnana kiil my self cuz i think she dosent luv me any more..can somone please tell me whats going on? and do you know this feling? and what could i do to make it stop?