Trust in yourself that you can help, and your willingness to do so is the most important thing you can offer your friend right now. But - and this is a big but - you cannot do this alone. A good place to look for information is at the National Suicide Prevention Lifeline's website www.suicidepreventionlifeline.org. You'll find information about warning signs, and a phone number to call for support.
This is a secret that should not be kept. Find a trusted adult, and share what you know. A guidance counselor, favorite teacher, school nurse, your parent, their parent - are just a few examples. If this doesn't work out the first time, find another, and another. Keep it up until someone hears you - really hears you. Ask that your school offer training for students, and staff, in how to help friends who are thinking of suicide. The American Foundation for Suicide Prevention offers "More Than Sad" for just that purpose. More information can be found on their website at www.afsp.org.Make sure your friend knows how much you care about them, how important they are in the lives of others around them. If they are in treatment (counseling or on medication) support them; encourage them to continue. Plan social activities around their schedule, when possible. Last, but not least, take care of yourself - both physically and emotionally. You are, after all, "friends for life," are you not?