I am still legally (?) married to my husband who abandoned me and my son over three years ago. I have been in a relationship for 18 months with a married man who is separated from his wife for at least 2 years. I am currently 4 months pregnant with this man's baby. I wanted to know, before I give birth, what had to be done in TN in order for the biological father to be on the birth certificate.

At this point nothing can be done, you needed a divorce before pregnancy. At this point, legally your husband will be the legal father of the child.

He will have to contest this in court after the birth to allow for the bio father to be shown the legal father.

Let me add that I cannot locate my husband.

So why haven't you filed for divorce? You don't need to know to get a default divorce.