Indian mother n Australian father of my Australian citizen 6 months old baby's custody.

I am an indian citizen but my husband is an Australian citizen , my marriage is 1 1/2 year old and i have a 7 months old baby who has Australian citizenship, My husband married me by fraud, he kept hidden his divorce status from me at the time of marriage as he was earlier married to an Australian citizen, the first copy of my marriage certificate shows that it's his first marriage but which was later modified with my consent after informing me. But now after the birth of our child he is mentally harassing me by constantly threatening me of taking away my daughter from me to australian and making me fight her custody cases at my city, at his home city in india and at delhi Australian embassy. He is blackmailing me with constant threats of suicides and it seems he is mentally unstable and has some mental disorder, he once physically abused me. I have all the proves regarding his mental instabilities and his threats to commit suicide and leaving a suicide note against me. His parents are also not helping me because they are confident enough that my ignorance regarding Australian and indian law will subjugate me infront of their blackmailing. kindly guide me regarding the Custody disputes between couples with different nationalities as i am indian and my baby and husband are Australian citizens so he blackmails me that all his case expenses will be beared and case will be fought by australian government and its me only who will have to suffer with 3 different cases at 3 different places as well as follows financially woes. please guide.