Good Company by Cynthia D'Aprix Sweeney

 Flora meets Margot then Julian while living in NYC. All three become actors though Margot has the most career success. Flora eventually focuses on voiceover work so she can take care of her and Julian's daughter, Ruby, and keep the family afloat and covered by health insurance. She thinks they have a great marriage--until she discovers Julian's wedding ring in the bottom of a file cabinet--a ring that he said he had lost swimming years earlier. Then doubt begins to creep in. Then she finds out Margot may know something about this. Plus Ruby is getting ready to head off to college on the other side of the country. So Flora feels the foundations of her entire life starting to crumble. The book is mostly a character study of Flora/Julian/Ruby/Margot and her husband David. 

I thought the ending was kind of abrupt and I wasn't sure what Flora was going to do next--though I was kind of tired at the time, so I should probably read the ending again in case the author's intentions were clearer than I initially thought. I liked Flora, so I hope things turn out well for her.