girlfriend of an alcholic

Yes, you are in over your head but it sounds as if you love this man and want him to get better. I understand that! If he is showing signs of alcohol withdrawal, which it sounds like he is, he cannot get sober on his own. He has to have a medical detox. Alcohol withdrawal is known as the DT's which stands for Delerium Tremors. Those tremors are the shakes you described. Now, not to scare you but please understand that there are two kinds of potentially life threatening substance withdrawals. Alcohol is one and benzodiazepams (valium, xanax) are the other kind. He needs to be monitored by a doctor and medical staff to be sure he withdraws safely. Plus, they can offer treatment and medicine that will make him more comfortable during the detox process. This will increase his odds of staying sober. Chances are, if he attempts to detox at home, without medical support, he will relapse and drink again. His intentions are probably honest and true but the strength of his addiciton and dependency are likely greater than his will. Getting and staying sober for him is not about willpower. Willpower is an ingrediant but not enough to ensure success on its own.
My best advice to you is to bring him to the emergency room of you local hospital. They will assess him and possibly admit him for detox. They may choose to send him to another detox center instead of admission there if they don't have an available bed or the resources. After the initial detox period, someone will offer to help coordinate in-patient treatment for addiction, if necessary or in other words, referral to a rehab. There are also the options of out-patient treament and/or support groups such as 12-step groups. Detox will only cleanse his body of alcohol. It will not address his brain and his addiction. Without addiction treament, following detox (they aren't performed at the same time), he will likely not stay sober for very long.
He is lucky to have you caring for him and loving him but please remember that his illness will not be cured with love alone. Many people think that they can help an addicted loved one by loving them more and more until they no longer need a substance to feel happy and well. You cannot change someone's basic make up and you cannot love away the trauma or hurt that someone has from before your relationship. You can no more wish away his alcoholism than you could wish or love away cancer, if he had that. It is a medical issue that must be treated professionally.
Good luck to you both!