I also fell through fonication many times with my girlfriend. Now I am working to stop because I know it's evil before God. I must stop it. Can God forgive me for what I have done when we repent?
"For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. For God did not send His Son into the world to condemn the world, but that the world through Him might be saved" (John 3:16-17).
Why do you think you are an exception to this rule? God doesn't offer salvation because people are deserving. God gives salvation solely because He wants to do so. "I, even I, am He who blots out your transgressions for My own sake; and I will not remember your sins" (Isaiah 43:25).
You are correct that the sin has to stop. Either you must make it very difficult for yourself to sin or you need to get married. "But I say to the unmarried and to the widows: It is good for them if they remain even as I am; but if they cannot exercise self-control, let them marry. For it is better to marry than to burn with passion" (I Corinthians 7:8-9).
Along with that, you need to become serious about serving God as a true Christian. See How to Become a Christian.