Need help, abusive husband (Mexico City)

I'm an American married to a Mexican citizen. We live in Mexico City. My husband is verbally, emotionally abusive and lately it has escalated to physical violence. We got married in the USA. I would have left this situation if it wasn't for the fact that we have a son together. Our son was born in the USA. I can't just up and leave with my son because he will get the police involved. I was wondering if you guys have any advice on what to do or where to go get help. I want to be able to leave the country with my son legally. I can't take this anymore. Sometimes I think the only way out of this nightmare is killing myself but I love my son too much to do that. Please help me. Sorry if this is all over the place, I'm very emotional at the moment.