My Boyfriend’s Mental Health

My boyfriend has some pretty serious depression issues. To the point he gets nearly suicidal (saying things like he doesn’t know if he can make it through the summer when we go to college, that kind of stuff). As someone who has been through mental illness myself, and someone who loves him, I want to help him through this. But I find there are certainly times when I don’t know what to do. Playing on this side of the field in mental illness, as in being the support not the patient, is kinda out of my league. Does anyone have any ideas for ways I can help him?