Husband having an affair, being abusive at home

I've been married since 5.3 yrs and we have a 2.9 yrs old son. It was an inter-religion marriage (I'm Christian and he is Hindu). A few months after we got court registered he started becoming aggressive & violent. Things were good after we had our baby but just before we could travel to the US last year his behavior changed completely and was treating us like he didn't want us anymore. His traumatizing behavior continued and he wasn't providing for us, didn't care for us at all when my son & I were very sick, I had to fight for us to be taken to the hospital. A couple of months ago I found out that he's having an affair (have sufficient proof and he admitschis affair which still continues) and figured out the reason behind his abuses and ill treatment. We are still in the US, abusive behavior continues, I'm forced to take up a small job that gives me very little money to buy some groceries and take care of my child's day to day requirements. I want to know what legal action can take while I'm here in the US? What do I need to prepare myself with when the divorce is filed? He is currently waiting for our visa processing to be complete and then I have a feeling that he will file for divorce or force me to do it. I'm worried about my child and having custody, what steps do I need to take to prepare for it? Also, how long would it take to get a divorce after it is filed and will I & my child be provided for? He has not made anything in my name, all assets are in his name, am I eligible for anything? I don't know my rights & what I'm eligible for, pls help. Kindly keep this question private.