I can not tell you what to do. I can tell you that when I first thought of killing myself I was 9 years old and wanted very very much to tell the principle of my school. She was the one person who noticed that something wasn't right and would ask me what happened to that happy person from before, I wanted to tell her but I let my fear keep me silent. In high school I was so depressed I was hallucinating, still I let my fear keep me prisoner. I didn't ever tell anyone until after I tried to kill myself at 27 years old.
I often have wished I would have overcome my fear long ago and had told Mrs Frost, the principal. I would have gotten help because she would have made sure of it. Yes it would have been hard, embarrassing but my life would have been so much easier. If this teacher is someone you trust, do tell her. It might cause some hard moments but overall I think your life will be much better for it.