Abusive relationship help please

My daughter is now 8 months old but my postpartum depression is bad. Will it get better. Even since my daughter was born I did everything. I got up everytime she cried or needed anything. My husband never helped because he told me that in Mexico a woman job to have kids and just take care of them by theirselves. I finally told him I can't do this by myself anymore. I told him I have other mental illness and he promised my OB/GYN that he would help so I could sleep at least 5 or 6 hours and that has never happened. I feel like snapping the fuck out on him and telling him that I am done. I felt like giving up but I would never do that to my daughter. Every time I tell his mother she just says oh he is tired. In my head I say bitch i am tired too and i can't do this by myself anymore. The other I when to a therapy appointment so I can't be mentally here for my daughter and my husband called me 20 times because he doesn't know what to do with her. I left at 12pm and got back home at 2:30pm, he never fed her or changed her diaper. She was crying because she was sitting in poop. So I asked him why didn't he do anything and he started getting physically abusive. When he cooled down he said he was sorry and he never ment to do that. When his mother got home I told her and she laughed at me and asked her son and he said it was all in my head. I tell myself all the I will leave but I know I will never leave. I will die in this relationship and I told my mom and I wrote in my will that my daughter will go to mom. Why do I let myself be treated like this. Here is what happened yesterday my husband had someone pick him up to buy adderall and when he came home I asked him about and i was holding out daughter he slapped my face. I wish i was strong enough to leave. I hope I don't die by this weekend.