Should I give her a second chance

Yup I agree with joecollege. You need to be able to trust someone if you're dating them and I don't think you'll ever be able to trust her. Its not hard to find someone who won't try and f*** your best friend. Its also not hard to find a best friend who won't try and f*** your girlfriend.

No way in the world. Drop her and drop your friend (unless he was the one who stopped it, even then I would still be very wary and keep him at arm's distance for what he said to her). Do not sacrifice your dreams for a girl, very least of all this one. They will have sex after you drop them ( you will see the blatent lack of loyalty even clearer then). Don't sweat them though, better you found out early that they didn't care about you (care includes respect) before you got deeper in the realtionship. It is a blessing in disguise. You will meet girls better than her when you go to california. It may take time but life will go on.

btw, no one gets "confused" enough to want to sleep with thier BF or GF's best friend. Did you tell her you were breaking up when you moved?