I admire anyone who is willing to take on the monumental task of raising a child , you are special people who do this.

To take custody away from a parent is a serious issue, very serious.
If he is a detriment to the well being of the child or their safety then it is the right thing to do.

Because you think the father is not well suited to raise his child does not make it a fact.
You allege he is a drug abuser . That definition can be placed on a myriad of people from all walks of life.

It is possible to abuse alcohol or other drugs and still be a decent parent. It is not common but it does happen to "functioning addicts" .
Not that I am promoting this kind of thing , it happens.

How is he unsuited for parenthood other than the substance abuse?
Does he have a job? A place to live ? Do you think he loves his son?
Are you qualified to make this judgement about any parent?

If there is enough evidence to show the father unfit,the courts will take the boy away, most of the time, and to place them with a family member is usually a favored method where possible.

I would get a good attorney now and have them counsel me on what to do and how to do it.
This is far too important to guess at anything. Be well informed about what you do.

Bless you for thinking of the welfare of a child, and may your choice be sound and your intentions true to the well being of the child.

I wish you well.