How to break up when your in a long relationship?

Ok i almost never do this (use yahoo answers). but my friends are asleep or at work right now and im desperate for some advice. Im 16 and my girlfriend is also 16. Weve been dating for two years and recently we have had alot of bumps. But i always seem to do something wrong or she always tells me she loves me but i never make her happy. she rubs it in my face and tells me how are YOU gonna improve this relationship so she can be happy. and i do try soo much and it all just goes un-noticed. I cant see alot of my friends. and hanging out with any girl is out of the option. I LOVE HER TO DEATH. i love her so much its ridiculous. but the only thing on my mind is to break up with her cus shes acting like an such an ***. i know she loves me but she just doesent know when to stop i guess. the only reason im hesitating is because if i see her with other guys im gonna get jelous. she pretty and fun but i cant be in something like this anymore. I want to break up with her but i dont know how to aproach it. can someone please help me out :( ?