Hi Im 54 Yrs Old. I Was Married For 27

Hi im 54 yrs old. I was married for 27 yrs. He left for a younger woman. I had a nervous breakdown, and i tried suicide 4 times. After being on my own for 3 years i moved in with my sister. She is older than me. Never married. she is mean, nasty and thinks im her maid. I work and pay her rent. I have no way to get out of this dituation, why is she so nasty?