I have a Facebook account (mine) that uses my cell number to login. Recently my girlfriend created an account using her email address, but it required her to add a cell number so I gave her my cell number and verified it by putting that code and stuff and her Facebook account was created. But now when I try login in with my phone number, it takes me to her account. Where has my account gone to?
Your girlfriend probably needs to disassociate your phone number from her account.
There should be an option to remove the phone number.
However, it's possible that by using your phone number that phone number has been removed from your account, so you would need to log in with your username or email address.