I think this might be the key to his depression:

    I put up with a lot of startup bullshit...

Stress symptoms don't necessarily manifest themselves immediately. It might be something that happened long time ago (3 - 6 months) surfacing now. And when it is happening, you might not pay attention to it, you might be inclined to overlook. (citation needed)

    50% is not wanting to put others through torment.

This is BS. Committing suicide with certainty and without much pain is hard work. I know, I had done my homework. But a good programmer should be able to come up with better strategies than walking into the traffic.

Besides why do you care? You'll be dead.

    There is no other 40%.

I think the other 40% is because you know subconsciously that you can actually go on. You just don't know how. Still, it's preferable to be alive than dead. Call it will if you like.

I hope he can change his circumstances and get rid of the depression real soon.