I am afraid to say I am suicidal?

Continue with the therapist until you uncover why you have these feelings. Or if you already know why, you may be more ready to tell someone than you think. Every time you get these dark feelings, think them away with positivity. Eventually you'll get used to these positive feelings and they will smother the other ones. Tell yourself about the value you hold as a person. Seriously. Everyone has value. I was in a emotional place similar to your own when I was younger. Thankfully it never got to suicidal thoughts, but it would have.