My sister is ill and her boyfriend, the father, is not a well suited father and his very choices he makes in his life make him unsuited.For instance, he is a drug abuser. My sister knows that I am going to try and get custody but her boyfriend, the father, does not. How can I get custody of my nephew?

Wow, bad situation. If you are all living in the same state and you can get your sister to corroborate the circumstances, the best thing to do is start a file with your local authorities and/or Children's Services. You can also request that you have your nephew live with you as a foster care situation. Please be aware that these are difficult times, but the important thing is to protect this child. Best of luck and hope things work out well for all involved. Be strong.

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.

The first thing to do is speak to an Attorney. These matters vary by State. The father is most probably #1 in line when it comes to custody. Grandparents are very often #2 in line. The fact that your sister is going to give you guardianship (which I would guess you are asking about) does not mean it will happen OR happen easily.

I would do NOTHING without legal counsel. Reporting anyone for drug abuse and getting CPS involved could very well get this child placed in a foster home while the details get sorted out.