Hey Isaiah.
I feel for you, little brother. You've made the first step toward healing already, admitting that you have a problem and seeking help to get out of it. I've walked the same road before you. Suicide isn't the answer and you are far from worthless. How can I know that? Because He created you and He makes no mistakes. He loves you more than you can possibly grasp. More than any of us can. With God, you can do this. You can be freed and healed of this addiction. But it might take time and it will take a persistent leaning on God. I have some tips from my own walk out of it that might help.
1. Every time, and I mean every time, you feel tempted to look at pornography(or any sin, really) use that temptation as a prompting to go directly to God in prayer and ask Him for help before you do ANYTHING else. Especially when you don't feel like it or feel like He's not listening. If your desire is to do His will(which includes repentance aka turning away from our sins), He will hear you.
2. After praying, fight back against temptations by turning your mind from it, by reading your bible and/or praising God until the temptation passes.
3. Do everything you can to avoid what might bring/have brought you temptation(sites, books, magazines, comics, games, music, tv, or anything with sexual or suggestive content). Anything you can access the internet with, have a parent install some sort of password protected browser app on the device that will filter out inappropriate content.
4. Try to get an accountability partner who you can confess your temptations to and ask for prayer. Do you have a father that you can have a man to man talk about this with? Or your pastor or youth leader? An accountability partner can be an incredible help. If at all possible, come forward to your parents about this. It might hurt them or anger them to know it's been happening, but I can almost guarantee you that it would hurt/anger them more if you keep it secret and don't let them help you out of it.
5. Remember that Satan is just as real as Jesus is and he /will/ try to lie to you. He can't /make/ you do anything, but he certainly will try to convince you to turn from God's path. He'll tell you it's not worth the fight. That you're better off giving up or killing yourself. To try to convince you that 'just once' is okay. Or that it's not a big deal. All of those things are lies, straight from Satan. All sin is a big deal and worth the fight to overcome, because it all cost Jesus His life to pay for it. There is no such thing as a little sin.
6. If you do stumble and fall, don't beat yourself up. That's not what God wants. What He would want is for you to turn away from it as soon as you realize you have and ask His forgiveness for it, then walk on in that repentance and do everything you can not to stumble into the same sin again. This is true for every sin there is.
7. Actively work on growing your faith and your walk with Him. The closer you are with Him, the easier it will be to overcome sin and temptation. Study your bible in your own free time, not just at church. Ask your pastor or youth leader questions if you don't understand something(that's what they're there for after all). Spend time talking with Him frequently throughout your day. Nothing is too small and nothing is too great to tell Him about. Don't forget to be still and listen too. He speaks with a small voice, through His word and through His Holy Spirit that lives in all Christians, that little nudging that tells us when we should or shouldn't do something.
This all might seem like a lot or overwhelming, but it gets easier with practice, trust me.
As far as depression goes, I've learned from experience that it usually stems from one of three things: Some sin we are participating in, from spiritual attack, or focusing too much on ourselves. When you feel depression hitting, check yourself(thoughts, attitude, actions) for sin. If you're pretty sure that you're not sinning, then ask yourself if you might be listening to Satan's lies about your worth. When you find yourself telling yourself that you're worthless/stupid/too far gone/ can't do anything right/etc, then pause. Put on the armor of God:
https://www.biblegateway.com/passage/?search=Ephesians 6:10-18. Then turn your mind to better things through study of His word or praising Him. This is what I do. I have a few youtube playlists of Christian music that are uplifting and/or are praising God. This is one of my favorites:
https://www.youtube.com/watch?v=D5wrwvn-f88&index=106&list=PLB91Pe4r9yYEeY-l5dtmlZB82hvMzkZ4w
With God, you can do this, Isaiah. I'll be praying for you and if you have any other questions, feel free to ask.