The first piece of advice I can give you probably seems like the last thing you want to accept. It's to try to detach yourself from the tangle of emotions involved in this. Back off a bit. Care a bit less. Cold and heartless? No, obviously it's important to still care, but it's also important, for both your sakes, to keep a grip on things and not panic. His life is his. If he wants to kill himself, and he does it, it's his problem, his fault, his responsibility. Not yours. If he does it, it's a tragedy, yes, but it's not your failure, it's his. Before you can do anything else, I would recommend you get focused and calm and achieve some kind of functional perspective.

Then pray for him.

Then try to reach out to him. Try to get a hold of him and get him some professional help (a school psychologist is a good place to start). You can be his friend, which may be important, but you're not a professional, and you can't just talk him out of his depression. He needs professional help, and getting him to see somebody is probably most of what you can do, other than simply providing your support and care.

Lastly, I do think you should take him seriously, but think about whether he's truly suicidal or merely throwing the idea out and seeing how people react to it. He's got a problem either way, but the latter is a bit less serious. I'm not confident that I have enough information, nor understand the psychology involved enough, to make this kind of determination. At the same time, I have to wonder if sending out email to a whole bunch of people with "I guess nobody cares" really just means "Show me you care." It's still a problem, still needs resolving through professional help, but it's means less cause (for the time being, at least) to worry that he'd actually go through with it.

I don't have a lot of experience with such things, but few except for professional psychologists/psychiatrists do, which is why it's important he see somebody with that expertise.

I'll keep the both of you in my prayers.