I don't want to give my girlfriend's credit card back.
Why don't you want to give it back?
She has credit card debts and she constantly uses my credit card to pay her bills.
Though she should not be using your card without your permission, it does not give you the right to do it back to her. This may be ground for her to take legal action against you in court.
She probably will take me to court, but I won't let her get away with this.
It sounds like if you just give her the credit card back, you can avoid going to court. Court and lawyer fees can be very expensive. It would be best if you could settle this out of court to avoid having to deal with the legal troubles.