I seen you talking about adultery on a web site answering questions.
I myself have the same issue. I'm living with my boyfriend of five years, and we have a child together. He is married to another woman, but they have been separated for ten years and he has not been able to afford a divorce.
I also am married but to a bigamist. He married a woman in one state, never divorced her, then came to my state, where we met and married. So I guess in God's eyes my marriage was a big affair, but the woman died later after we married. I don't have the money to annull my marriage right now. If my boyfriend and I do take care of our past marriages, ask forgiveness of it and get married, would we still be living in adultery? If so, I've prayed about this situation. Will God get me out of this situation, because every time I've tried to leave, something put a stop to it. I don't know if it's God saying wait, or what. I can see God is working in my life but this one sin keeps nagging me. I cry all the time, but I don't know what to do. If I lay it at God's feet and wait or what. I'm tired of doing things on my own and making a bigger mess.
Any advice is welcomed because I'm lost on what God wants of me.
Let's start with basic facts. Intentions do not matter; what matters are the things you actually do with your life.
You are living with a man to whom you are not married. Both you and he are legally married to other people. Therefore, you both are living in adultery. While you note that your legal husband was a bigamist, for all intents and purpose you and your boyfriend have done the same thing -- other than you have not tried to enter into another marriage. You took the pretend marriage route instead.
Your marriage both legally and according to God's law was not valid because he was married to another woman. However, since his former wife died, in God's law your marriage then became proper. "For the woman who has a husband is bound by the law to her husband as long as he lives. But if the husband dies, she is released from the law of her husband. So then if, while her husband lives, she marries another man, she will be called an adulteress; but if her husband dies, she is free from that law, so that she is no adulteress, though she has married another man" (Romans 7:2-3).
Since you abandoned your marriage later, and since you did not state why, I must assume that both you and your boyfriend did not leave your spouses because of their fornication (Matthew 19:9). That would mean that neither one of you have the right to another marriage according to God's law.