Prosecutors say 53-year-old Kirsten Smith is scheduled to be arraigned on a murder charge Monday in Brockton District Court.
Police responded to the couple's home on Friday afternoon where they found 52-year-old Scott Benoit suffering from a stab wound to the chest. He was pronounced dead at the scene.
State and local police interviewed Smith until late Friday, when she was charged.
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The Plymouth district attorney's office says a knife was also found at the scene.
Smith was held over the weekend and it was unclear if she had hired a lawyer.
The death was the city's fourth homicide of the year.