My mom said she isn't obligated to love me

Today is my 18th birthday and that is what my mother said to me. Through out my life I never felt like my mom cared about me. She constantly told me I was fat. She loved to call me a bitch. The first time I remember her calling me a bitch was when I didn't watch my 4 month old brother and he fell of the couch. I was 6. She got mad at me when I was 12 because she told me to clean HER room and I said no so she pushed me outside in the called and called me a fat cow. It was snowing and I was freezing. Today for my birthday, I was going to see my dad. I was going to take my car (which my daddy bought me). She said I couldn't go and I had to watch the kids. I told her I was going to see dad for my birthday and she said "I don't give a damn about your birthday." I got really upset and told her she makes me feel like she doesn't love me and my own mother said "I'm not obligated to love you. I took care of your ungrateful ass for 18 years. That should enough. There is no law that says I have to love you. You're alive so be grateful. " That hurt me so bad. I spent my birthday watching the kids while she went to the casino... Maybe my mom isn't obligated to love me, but I wish she did because I have never felt so worthless...