My son is 10 yrs old, and we live in Tennessee, my husband and I have been together for 9 yrs. The birth father's name is on the BC. My husband want to adopt my son. What are the best steps to take. I was never married to my son's dad.

I was never married to my son's dad.
That is IRRELEVANT.
You have to have his biological father's rights terminated.

TENNESSEE - §§ 36-1-113(g)-(h), 37-1-166(g)(4)
Grounds For Termination of Parental Rights
1.Abandonment or Extreme Parental Disinterest
2.Abuse/Neglect
3.Mental Illness or Deficiency
4.Felony Conviction/ Incarceration
5.Failure of Reasonable Efforts
6.Abuse/Neglect or Loss of Rights of Another Child
7.Failure to Maintain Contact
8.Failure to Provide Support
9.Failure to Establish Paternity
10.Child in care 15 of 22 months (or less)
11.Felony assault of child or sibling
12.Murder/Manslaughter of sibling child