I don't know how to cope

I've been in a relationship and it started out and has been pretty great, but recently the guy has been very depressed and feeling hopeless and it's had a major toll on the relationship. To the point he's pushed me away and I'm pretty sure is breaking up with me. I deal with depression as well, but I've been able to manage it when it gets bad. He however, keeps saying he wants to end it and that he's never happy and has just been pushing himself for me. I told him suicide is a permanent fix to a temporary problem, and that we will be happy together soon when we are done with school, but he's really lost and has even gone to rely on alcohol and smoking. I have tried so hard to help him but I don't know what to do anymore and it's gotten me so scared because I feel he is going to try to hurt/kill himself.