Dear sister.
My heart goes out to you. I can relate in many ways to you. A statement by Elder Maxwell gives me a lot of comfort: "Do not mistake local cloud cover for general darkness." The storm clouds you are in will pass! The day will become brighter. Light will replace the dreary darkness.
I have had many suicidal thoughts over the years. Two cousins of mine killed themselves. It is an awful pit to be in.
I have discovered many powerful tools that help: surround yourself with positive, uplifting family, friends, music, environment. Immediately go out and help someone today! Be of service. "If you are not satisfied with your lot in life, build a service station on it." When you are in the service of your fellow men, you are only in the service of God.
Put on the full armor of God; pray continually. Believe, believe, believe! "Lord, I believe; help thou mine unbelief." -- Mark 9:24
The stage of your mind is entertaining thoughts continually. Kick the evil actors off your stage by using Pres. Packer's timeless counsel to listen to worthy, uplifting music. Select favorite hymns and start singing when evil thoughts butt in on your stage.
One of the most powerful lessons of the temple is that Satan is a weak punk! He's smart, sly, and insidiously charming but he is dismissed when you seek the light! Get a Priesthood blessing today!
Everyone has sinned. Sin makes you feel worthless. Repentance brings sweet comfort and peace. I've experienced the awful bitter fruits of sin and basked in the peace and comfort of repentance.
The Atonement of Jesus Christ works, dear sister. Heavenly Father loves you!