I've never dealt with this before and I don't know what to do to help him but protect myself.
Lucky for you, the same thing will both help him AND protect you--get out of the relationship and away from him, totally and ASAP. Presumably if he is able to get alcohol to continue his binge, he is not totally without resources. If he threatens suicide again, call 911 and direct them to his house--they are professionals, you are not. If he turns out to be serious, they will know how to handle it. If he is NOT serious, they will know how to handle that too.
You are only 3 months into this, and there is nothing to keep you there except your own "need to be needed", which it seems you are aware of already. One of the things that is often discussed on this board is how dating is a time to see what someone's like and how we get along with him/her. Is this what you want to sign up for over the long term, especially when you consider that this is the BEST he will ever be? (Alcoholism is a progressive disease, and he WILL get worse as time goes on.)
Please, read around this forum as much as you can. Educating yourself about alcoholism will do so much towards helping you decide what to do. I'd also strongly recommend checking out Alanon for some f2f support for yourself. Both Alanon and SR can also help you get in touch w/that part of you that wants to "help" and "rescue" and make sure that you use those impulses in a healthy way.
Welcome to SR.