Can you tell me your opinion on my forked up family life?

Since my auntie died, my mother has been on a downwards spiral. First, she started getting a lot of piercings. Then, she started going to the gym every day (I have my suspicions that she had an eating disorder). After that, it all went to ship. My parents split. My mother acted like she didn't give 2 shirts and I have my suspicions that she was running off with another man whilst my dad was still in the house. She would stay out nearly every night. When my dad finally left, she told me that she was newly seeing this man from her work. The reason why I believe that she had been seeing him for a while is that she was already having sex with him. She was buying lingeré for months before my dad left. I also have found her lube and her handcuffs for their kinky sex! Now, she has gotten another piercing, and she got a stomach tattoo! She is also planning to get a new tattoo. I hope this isn't her new phase because if so, she will get one she regrets. Her and my dad never did stuff! She never wore flashy lingeré like she is now! She also has stopped acting like a mother altogether. She doesn't cook, she just buys a microwave meal. Everything I do I get ridiculed for. My older sister, who is 19, just listens and believes anything my mother says. I'm asked to do every flicking thing! Why can't my sister do any work instead of sitting on her bony **** all day! Can you please tell me what to do in my situation? I'm finding it extremely difficult at home and I need some help or advice.