i have been trying to get on the right path. I know I have sinned and was lost. I made mistakes. I am in a relationship, never married, but we love each other and would like to marry eventually. We have a child together. However, we both have children with other people. What does that say for my children and ourselves? I know it is a sin, but can we be forgiven? I know the Bible states you become one and have children together, but does it mean when you both have children together and children with previous relationships? What should I do?
I am assuming that neither of you were married in the past. If you are certain you want to marry this man, you should stop waiting for it to be convenient and get married. There is no reason for putting it off. The fact that you both have children from your prior sinful relationships has nothing to do with your ability to marry. Your sins were in the sexual relationships you had without being married. The children are not the sin.
"Becoming one" includes having sex and the children that naturally results, but becoming one is far more than the physical relationship. A man and woman become a new, single family unit when they marry. They are a couple and no longer two independent individuals. They work together as a family and make decisions together as a single unit.
God has said He will forgive all sins of those who obey Him. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9). There are no exceptions, there are only those who refuse to obey Him. "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9).
As an introduction to what you both need to do to have your sins forgiven, see: What Saves Us From Sin?