How to back off a relationship without hurting her too bad?

ive been with my girlfriend for 2 years and i love her very very much. we have a very serious relationship, and it has been like this for most of the time we have been together. at first she wasnt sure how serious she wanted our relationship to be, and i wanted to spend the rest of my life with her, now it seems to have flipped around.
we get along awesome, we're part of eachothers families and really match great. she had a few relationships before me, though i guess they were all jerks, i only really dated 2 other girls, with the longest relationship being barely 4 months. (i am 21 she is 18) i was always a very shy kind of person and prefered to spend time alone or with one or two people and didn't like the idea of just casually dating girls.
now i feel like i'm a completly different person, i want to go out and meet new people and try new things and not have any serious attachments to anybody, and i'm even thinking of moving several states away in a year or two.
i love my girlfriend and care about her more than anyone in the universe, i would love to spend my life with her and have a family and all, but at the same time i've been feeling like i never really got to be really independant and party and just mess around if that makes sense, and now i have that itch.
my girlfriend always talks about us in the future and stuff that we will do and whatnot, and i dont know what to say to those things. i feel bad going along with it because i dont really feel the same way, but i feel like i cant disagree because i was saying those things before her.
i dont know if im making sense, but basicly i want to back off the relationship slowly because i'm not 100% sure yet, but she means so much to me it would kill both of us if i just dumped her all of a sudden. I want to just bring our relationship down to a level where if i decide that is definitly how it needs to be, it wont be as shocking and upsetting and confusing.
thank you very much for any suggestions or advice, i really appreciate it :upset:

If you want to do it that way, start being "busy"... she'll get the message.

If you make her think that everything is fine when it really isn't, you're going to hurt her a lot more than if you just broke it up. I know this from experience. My ex was talking about marrying me two days before we broke up.

You need to stop going along with her future plans. Tell her how you feel.

Exactly my point! Words from my mouth! Very nice!

Men you may regret it, one of the best sayings of all time is: You never know what you got, untill its gone..its true we only live once and love comes just a few times in a lifetime. but if you really think its what you want then take the risk, but you gonna hurt her thats 4 sure

Braves, I say just be direct with her. It's going to be confusing and hurtful to her no matter how you do it. And breaking off with her slowly and over time will only string her along.

This is time that she could use to heal, move on, and find someone else.

Agree with Rubenblades.

Anyhow, me personally, say it face-to-face, honestly and respectfully. Make her understand why.

Strongly disagree with the just be busy until she gets the message. I find that dishonest and disrespectful. Not just to a lover, but any human being.

right now, i am in almost the exaaact situation. im 20 and my bf is 21 we met in high school and we have been together for almost 3 years. i love him and think i could possibly see myself marrying him and everything but right now im in my 3rd year at college (his current last semester) and just want to have fun a little bit, but i kno it would kill him. i actually tried 'taking a break' over the summer but that didnt work because he talked me out of it. i love him, but i want to go off and just explore a little bit and see how it is. its a little selfish, but i thats how i feel. but he said if we ever broke up, there is no way we would ever get back together, so thats why im still here. i dont want to lose him completely, just ... temporarily. i know im sounding stupid...

If you are going to moving to another state then that could be a perfect opportunity to cool things.

I DO understand what you are saying. You are obviously young and you want to experience life before being tied down. There is nothing wrong with that.