Abandonment by bio sperm donor a possiblity?

Hi. My situation is tricky, at least to me it is. When I got pregnant with my son 7 years ago, the bio ditched us when I was about 3 months along. I had phone contact with until I was about 7 months along and then nothing. He didn't call to check up on my son till he was 4 months old, at which time I let him see him. After that he has only seen my son twice and both when he was a baby. Also, my husband has been in my son's life since he was 8 months old. He is the only father he knows. In the past 6 years, the bio has sporadically contacted me to see if he can see my son, the last time being over 3 years ago. I told him last time that if he wanted to be a part of my son's life that he needed to do what ever he had to legally to be in his life because I was not going to let him just walk in and out and hurt my son. Nothing happened.And then 2 days ago the bio contacts my step mom and is asking to be a part of my son's life. He has never paid child support and is not named on the birth certificate. My husband wants to adopt my son, all we need is to save up the money to pay for the lawyer. What can I do for my husband to adopt my son and what rights, if any, does the bio have? Could I file an abandonment suit? What about his parental rights being terminated? Does he even have parental rights since he is not named on the birth certificate? I just want this part of our lives to be resolved. I would also like to add that we live in Idaho and the bio lives in Texas. Thank you for any advice.