I've been reading through a lot of other posts, and a lot of people talk about how their lives are terrible and they have nothing and no one and they feel horrible about themselves. It doesn't seem like that's how he feels, so that leads me to think that my being there isn't really doing anything at all.
I can differentiate at least six different types of depression/suicidality in my head right now, and only two or three have to do with that kind of thinking. It's a common misconception that there's only one kind of depression, and only one kind of suicidal. That said, you're being there helps no matter what the cause is, and it's probably one of things things that's kept him going this long. No matter what is causing someone to think about ending their own life, companionship and someone who cares being there for and with you always help. Always.
But your OP said this
His feelings have progressed from when he initially told me about all of this. He had been overwhelmed with college and the overbearing possibility that he would not succeed and become a deadbeat always burdening other people. He considered the possibility of succeeding in college, and then jumped to the difficulties of finding a job, and from there the stresses of a job. He tells me he understands that the struggles he'll face in life are worth it because he can live a happy and fulfilling life. But he is now exhausted and just wants a break from everything.
He basically feels (near as i can tell), that "I'm worthless, and life isn't worth living. I'll probably fail at it and everyone would be better off without me, and I'm tired of trying to succeed." That could be all there is, but I feel like there's more beneath the surface that either he hasn't told you, or you didn't have time to write out. Do you know how long he's been suicidal? Has he honestly told you what the thing that concerns him the most is? Because just a fear of not being successful doesn't seem like the thing that eats at him most. I've had a lot of friends that had that issue, and it was never just "i won't be successful"; it was almost always, "I'm not good enough. not at this, not at that...I am a failure in every way."
At least, that's what my experience has been when people say "I'll never be successful.'' It's something to ask him about though or consider...."Are you worried that you won't be successful, or is the real thing that you feel like a failure and worthless and that you'll never be good enough?"
I don't think there would be any final straw that sent him over the edge, but just the thought "hmm, today seems like a good enough day." He's so very logical about it, despite the fact that his final answers in our arguments are always along the lines of how he doesn't really care.
I don't think he's really that apathetic about death. That might be true, but i think it's worth asking if that's just the front he's putting up. I mean he certainly could be, but I'd look into it.
I will do and be whatever he needs, but it's hard not to be completely selfish and in a way make this all about me, because I don't want to lose him. I feel that if he does go through with this, I won't be able to move on from it and that scares me. How am I supposed to be more empathetic and selfless?
You need to be selfish sometimes. You're plenty empathetic and selfless as it is...don't put so much pressure on yourself to be some kid of perfect empathetic paragon of selfless magicalness. If you weren't a little bit selfish, you wouldn't care that he died so much, because he's important to you, and you don't want him to die, because you love him and want him. It would probably make him feel pretty good to tell him that, even though probably it won't change his mind.
I can't see his pain, but I've been trying to resolve myself to support him with whatever decision he makes
That's the thing that helped me the most. Knowing that there was one person that didn't believe that certain choices were wrong and other right and there was only one acceptable choice they would support.
I don't want to bury any of my feelings down because our relationship has been wonderful simply because we communicate, but it seems like the only way I could be selfless is to just pretend I am, just pretend that I support him in that decision even though I see no way I could. I don't want to do that though.
Don't bury feelings. I agree, the beauty of a relationship is that you two can communicate openly. You don't need to be selfless. You don't need to pretend that you're okay with his suicide or death, and you can full well tell him that....support (when i say it in this context) doesn't mean "I agree with and advocate for every decision you make because you can do no wrong"....it means "I love you and I'm not going to hate you or chide you or dislike you or stop loving you, just because you do something I don't want you to do.''
"support" doesn't mean "agree with and be cool with and don't tell him you don't like it." it just means that he knows that whatever he does (in this context, not everything), you aren't going to beat him over the head (emotionally) with a stick that says "that choice is wrong, it's bad, it's evil, i don't agree with it and if you do it, i'm going to stand on some high ground or love you any less or be disappointed in you."