It is not true that someone who talks about it won't do it. Often that is a clear call for help. Drugs or alcohol are involved in two out of three suicides. Use of these chemicals intensify the already-existing feelings of helplessness and hopelessness that the person is experiencing. Few people who end their lives are mentally ill.
Most suicidal people are undecided about living or dying.
Happily, most are suicidal for only a limited time and, if prevented from destroying themselves, go on to lead useful lives. Although some people hide or mask their true feelings, and never give clues most people do give clues to others through their behaviors. Take threats seriously. The person is asking for your attention. In which you felt sad and hurt, or scared.