need some relationship advice

okay i have been dating this girl for about 5 years now we have been through more bad than good. it first started out as more of a physical thing (the only girl ive been with) and then it started getting serious. shes very over protective of me, i dont think i can handle it anymore...
Examples: i cant go anywhere with my friends if theyr bringing their girlfriend along with them, i had a poster of britney spears up in my room and she threatened she would break up with me if i didnt take it down (the threatens me with that all the time), she'll ask me when were watching a movie if a girl is cute or hot and if i say "ya shes okay" every time that girl in the movie comes on she tries to make me close my eyes, she goes through my room and burns what she dosent like when im not around.... i have to keep a constant eye on her when shes at my house, shes always telling me im stupid...shes embarresed of me and stuff like that (one time i went to a bank drive through and cashed a check... after i got the money i pulled up and counted my money just to make sure i got the right amount... and she told me that because i did that i embarresed her Sooo much), and many many many other things but they would make the post too long.
and personally im starting to think shes getting physically less attractive to me.
i met this girl thats a niece of one of my friends shes 17, she is really really cute, she likes a lot of the same stuff i like (unlike my g/f... well not really my g/f were just seeing eachother) she works at McDonalds and when i go there its i cant be sure but i think she likes me cause she jokes around with me and seems excited that i came to visit her...... if i would think of my perfect girlfriend she would be the one i would think about.
i just dont know what to do, i mean me and my g/f have been together soo long i dunno if i can handle being with out her, all my friends and her friends thinnk its all down hill from here with her but i dunno im just scared of a change we do everything together. do you think i would have a chance with that other girl, but most importantly what should i do about my girlfriend...

im asking the girls because you could tell me what might be going through her mind???? guys can answer this too

Ps: sorry so long