My sons best friend told me he wants to kill himself

My sons best friend messaged me earlier sending screenshots of my son talking about killing himself last night. He said he had talked him out of it but that he's mentioned suicide to him before but my son made him promise not to tell anyone, but he was scared because last night my son came really close and he's worried about him. He also told me my son had been self harming and he's the only one who knows. I had no idea he was so depressed and I have no idea why. He's been excited about starting High school next year, he maid the honor roll for his 8th grade class. His friend did mention that my son told him he feels like I put too much pressure on him to be perfect but he never once told me any of this. I wish he told me because I would never want to be the reason he's hurting. How can I approach him about this? What do I say and how do I go about everything?