Can you tell of someone is going to commit suicide?

Recently, my brothers friend commited suicide. Everyone was shocked because he always looked so happy. He did call my brother to tell him about his relationship problems but my brother ha to start work so he couldn't finish talking to him. After work, my brother tried calling him but he wouldn't answer. A day later, his friend hung himself. So I'm asking if there's any signs because my friend gets depressed. She says she can't take anymore of stress with this guy she talks to. She doesn't like him and she can't figure out why she still talks to him. There's nothing I can do but tell her to cut ties with him. She keeps saying she did that 15 times but she's too forgiving. It makes me scared when she says "I can't deal with it anymore." This guy just starts arguments with her all the time and then she gets annoyed when he ignores her. I can't figure out why she talks to him if he's causing so much problems with her. She doesn't like him as a friend too. She also has low self esteem.