Selfishness gets a bad rap. Who wants to be around someone with no goals or desires of their own? Be brutally honest with her now, and you'll probably remain on good terms, which, believe me, you'll grow to appreciate. As for my experience, I got into a serious relationship in college before I was ready for it. It was much easier to start than it was to finish - she was an incorrigible drama queen, and there was never "a good time to leave," and I thought selflessness was somehow honorable. I could have saved us both a lot of time and bitterness if I'd bailed as soon as I started having my doubts. If you really want to take the low road out, start insisting on sex acts you find on Urban Dictionary.