The most important thing I can tell you is that God loves you - and because He loves you, He yearns for you to leave the dead-end road you're on and come back to Him. He knows the price you've paid for leaving Him out of your life and going your own way - and He doesn't want you to have to pay it any longer.
This is why He is willing to forgive you, if you will only turn back to Him in repentance and faith. After all, Jesus Christ has already paid the price for your forgiveness - the price of His own blood, which He shed on the cross for you. Satan will try to convince you that you have gone too far - but it isn't true. God's promise is for you: "Let the wicked forsake his way and the evil man his thoughts. Let him turn to the Lord, and he will have mercy on him, and to our God, for he will freely pardon" (Isaiah 55:7). Accept His offer of forgiveness today.
Then take steps to grow strong in your faith. Think back a minute: Why did you fail to keep the commitment you made to Christ when you were younger? The main reason, I suspect, is because you didn't grow in your faith, and when temptations came, you gave in.
Don't let this happen again. Get in a church where Christ is preached and lived; commit everything to God in prayer; let the Bible's truth saturate your mind and heart. The Bible says, "Come near to God and he will come near to you" (James 4:8).