My wife have deserted me from past 1.5 years along with my 2.8 year old son

Dear Sir / Madame We are married for 6 years now, we have a 2.8 year old son. Due to misunderstanding in the family my wife started resisting to visit my parents who were living in my native and resisting to show the child to my parents. She wen to her parents house 1.5 years ago along with my son, I vaccated our house and started leaving with my parents three months later as she refused to return. Now I am leaving with my monther in my native, my father died of an heart attack 10 months back due the mental harrassment by my wife & her family members, they went to police sation several time threatening our family even for small reasons, many attempts failed to convince my wife and their family to leave together peacefully. Now she is not leaving at her native she is leaving in Tamil Nadu alone leaving my son with her mother in her uncles place, very recently i leaned that she is having an affair and she is ready to give divorce and not letiing me to see my son. Kindly guide me in this case what should be the next legal procedure to get the custody of my son as he is not getting necessary care and attention. Thanks & Regards