How to get custody of the child without divorce

I am working in s/w MNC as project manager in Noida and is a mother of 4 year old son . Working exp of almost 11 years . Currently bein separated for the past one year . Reason of separation husband being into Drugs (Ganjha),alcoholic,adultery and domestic violence being supported by mother in law and sister in law . Now I take complete responsibility of my son and not even asked for a single penny from my husband for the past one year . Recently , he is threatening me of filing child custody case i.e. visitation rights of sat / sun that too in my absence for which I never agreed . As I put condition he and his family can only meet my child in ,my presence because of his bad habits . Please let me know whether he will get the visitation rights in my absence even he is been into bad habits . I have already filed the police complain but not FIR as I seriously don't want my son and myself being into all this . But now he has started threatening me.Noted-He is also a lawyer-pratyush sahay