Is there any way my husband can adopt my children since he has been the only father they really ever had?

I have been in a custody battle for about 4 years now with my ex-husband. My ex-husband has lost custody because he overdosed with the kids in his care and assaulted my new husband who has been helping me raise my children since the oldest was 2. My husband has been the only support my children has had and my ex has never provided child support, overdosed with the children in his care and assaulted my husband at a supervised visit. Now, I found out my ex was convicted of assault.