Well, if you really love this girl and what she has done isn't that bad and you feel you could understand what she did and why and she promises not to lie again you (in my opinion) should take her...
If your friends a true friend then she wool hopefuly forgive you. just tell he what you've done and maybe make her a little card to tell her how sorry you are, don't worry, she/he will forgive...
Neither "I gone there once" nor "I been there once" are correct. One would say "I have been there" or "I've been there" OR "I have gone there" or "I've gone there". As for "I was there once" and "I...