My close friend wants to commit suicide. How talk him out of it.?

He was one of my best friends. Recently he just got out of a breakup with his girlfriend. He wanted the pain to go away so he started to like my girlfriend. Then he started messing around with my girlfriend. I got angry with him, and he got even more upset. He said he couldn't think, he just wanted the pain to go away. I keep trying to convince him that time will make the pain go away, and that you don't kill yourself over a girl. But he just wont listen. He's been sending me these long messages saying he's going to kill himself. And he's been posting things on tumblr. I don't know if he's really going to do it. But if he does I think I'm the only one who can stop him. I asked him what will get him out of it and he said the only thing is him getting back with his girlfriend. Him and his girlfriend love each other still, but they broke up because of the distance. I tried to talk to his girlfriend but nothing is going out the way I planned. He says that all he does all day is cry because of the pain and he wants to kill himself because of it. I him to talk to the suicide hotline, but idk if he'll do it. His mom knows but Idk if she's doing anything. All she said that she was really worried. I need some help. Please!