Full custody- no contact for two years. Junkie father.

My sons has not seen his biological father in two years, he is only 4 now. The past 3 years, his father has been on drugs (Ice), become homeless on and off, multiple outstanding warrants which resulted in his going to jail for a few months and he is now out on 12 month probation with regular drug tests. I am now married to a wonderful man who has taken on the father role with ease, they have a really strong bond which formed very naturally and my son calls him dad. My son does not know his biological father, I showed him a photo recently and he did not know who it was. I recently made contact with the bio dad to ask for a signature on a passport form to renew my sons passport and he is now asking to have a relationship with the child. I said not until he gets his life together and so now he is refusing to sign the passport renewal form. I am going to see a lawyer but I am after some advice or stories on other people’s experience with the family courts and drug addicted and violent parents. I am going to be asking for full custody as my son is not safe with his bio dad and it will do more harm than good to even have supervised access. When the bio dad was not around my son was constantly sad that he didn’t have a dad and he is now thriving with my husband.