I am currently married to BF, and 16 year old step son lives with us (3rd time now) after his BM kicked him out and said she never wanted to see him again. BM has legal custody. Unfortunately I am planning on divorcing BF. My step son states that he wants to live with me, not BM or BF. Son talked to his BM and she doesnt care where he goes as long as it is what he wants. We reside in Illinois and I was wondering if I need the BM to sign a guardianship paper or how to legally proceed so that stepson resides with me. BF and I have been married for 2 years but have been together 9.