Lord CAL,
I would be interested to know how old you are as you seem quite concerned with your level of experience - - I think that experience, or lack thereof, is only a big deal if you make it one. I've dated men, all throughout the spectrum of experience levels and I can honestly say it IS an issue now as I am hoping to find a relationship that will lead to marriage - - earlier in my life it was not remotely an issue.
It is time for you to learn a sad reality of life though - sometimes it is better to cause someone some "minor" heartache now rather than some MAJOR heartache later. The feelings you are describing indicate that you are feeling smothered and that you are not in love with this girl - - out there, somewhere, is someone who might be able to fufill her needs but she won't find him while she thinks you are him. (Likewise out there, somewhere, is a girl who will be more confident in herself and therefore will be able to give you the space that you need - you won't find her while you are committed to this girl.)
Your ability to maintain the friendship depends on how you break up with her and HER level of maturity. I have just watched a very painful breakup between two people - he a mature adult went to her house (after three weeks of dating, one of which he was out of town!) and said he just felt she needed more than he could give her. She is now IRATE and HATES him. So despite his attempt to handle things maturely - her lack of maturity means that friendship will not be possible. Your situation may be the same OR you could tell her she needs more than you have to give, but you would still like to offer her your friendship and she could see that you are looking out for her best interests and think that alone will make you worth having as a friend.
I guess I have kind of taken this all over the place, its late, and I have lots of thoughts, the short of it is---break up with her, as kindly as possible, as soon as possible, there is a whole world out there. You will only gain experience by going out and living it.
Good Luck-
Jules
I think the mistake a lot of us make is thinking the state-appointed shrink is our friend. - Jack Handy