Just me,
After reading through you post, I can honestly see that you are very confused. This is a traditional Catholic forum, not a NO forum and you will get very different answers I am afraid.
Hopefully this will help you understand things more clearly.
Once two people are validly married, they are always married. When these two people divorce, neither of them can ever get married again, unless one of them dies. Marriage is until death. Dating a divorced person is adultery.
In certain cases, however, the Church can be asked to determine if there actually was a marriage to begin with. This is what happens in the process of annulment. Presently, the NO Catholic church in America grants a lot of annulments. It is quite arguable if these annulments are actually deserving or not.
Criteria for annulment is quite serious--mental illness, drug/alcohol abuse at time of marriage--etc. Just because two married people have problems after their marriage does not invalidate a marriage.
I understand that you friend did not ask for a divorce. He was basically abandoned by his wife. This is a sad situation, however this does not give him license to enter into an adulterous relationship with another woman.
You, personally, have only one option. That is to abandon all ideas that you can have a sincere relationship with this man. He is married. Even engaging in a friendship with him might lead to something sinful. IMO, it's best to leave it alone.
Your friend has other options. He can attempt to reconcile with his wife (which is the best option, especially if children are involved), he can seek and annulment (which he'll probably get in the NO), or he can remain single and celibate.
Hope that helps.