McCormack threw Morris -- her husband of 10 years -- out of their Los Angeles home Sunday night after he told her photos of him embracing McPhee were about to be published online.
The Post said Morris attempted to buy the photos to keep them from being seen but was unsuccessful. The images were widely circulated this week and McPhee was a top trending topic Thursday.
"Mary threw Michael out of the house on Sunday night when he told her that TMZ had the photos and that they were about to be released," an insider told the Post.
McCormack was part of the cast of the recently canceled "Welcome to the Family." Her other small-screen credits include "In Plain Sight" and "The West Wing."
McPhee, a former "American Idol" star, is separated from her husband, Nick Cokas.