Custody of child

Respected Forum, My wife give me divorce (at notary on Rs.100/ stamp paper) after 11 years of marriage. We are inter-caste love marriage couple both are belongs from Hindu family. Our marriage was done in a notary and after that reception was arranged by her side. I have a child also, he is above 8 yrs now. But before 3 yrs in the name of job and study she leave him at her parent's home in other city about 400 kms away since then he is living there, But in May 2016 suddenly she told me she got a job in another city and now she is leaving me and to sign the above said divorce deed at notary. Its unexpected for me, if I know her plan before why I allow my child to send her parent's house. 1- I want to know is the divorce at notary on stamp paper is valid or not ? 2- If I go for custody of child and If court ask to choose among the parents, I afraid he is with them since last 3 yrs and I meet him in 2-5 months so they easily motivated him to not live with me. If court allow me to keep him just for 01 yr I assured that he never wants go with them. What the court should do in my case. Please help. With regards