My friend blames himself for everything; now he is considering suicide...

You can’t save him on your own. and I don’t think we can really do anything to help you do that. If he is considering suicide, you need to get him professional help. Refer him to a therapist, the hotline (probably best) 1–800-273–8255 or, if he’s under 18, his parents.
If you think he is in serious danger, call the cops.
I don’t mean to be negative, but if he is telling you he is considering suicide, he is seeking help. People don’t talk about killing themselves, joke about it, etc if they aren’t looking for help.(usually) If he already had his mind made up, he would do it without mentioning it.
You need to get him help if you are worried or if he is considering it

Even if you are worried about him hating you/whatever. It’s better to be safe than sorry

We don’t have any of the specific information on why your friend feels “responsible” for any particular situation.

You should call the suicide hotline right now. Don’t wait. They are equipped to deal with this type of situation.

1(800) 273–8255.

@SergeantQueen is correct. He is seeking help by telling you. Get him in touch with people much more qualified than us to help him. Most cities have a suicide hotline. Find out what it is.
This is a serious matter and should be treated as such.
Good luck

Yeah… You need to call 1(800) 273–8255 and ask them what to do. Don’t tell him to do it.

And I say this as a person that thought I could help and I couldn’t. It has haunted me for 25 years. Pass this shit onto someone else.

If it will help you to refer the phone number, that’s 800–273-TALK.

Good luck.

Take him to the nearest Hospital . Explain to the Doctors.
He tells you as you are probably the only one that he can confide in.
You are his friend.