The Fake by Zoe Whittall

A scammer as alluring as she is elusive irrevocably upends the lives of two strangers in this gripping novel from the acclaimed author of The Best Kind of People.
After the death of her wife, Shelby is suffering from prolonged grief. She's increasingly isolated, irritated by her family's stoicism and her friends' reliance on the toxic positivity of self-help culture. Then, in a grief support group, she meets Cammie, who gives her permission to express her most hopeless, hideous feelings. Cammie is charismatic and unlike anyone Shelby has ever met. She's also recovering from cancer and going through several other calamities. Shelby puts all her energy into helping Cammie thrive—until her intuition tells her that something isn't right.
Gibson is fresh from divorce, almost forty, and deeply depressed. Then he falls in love with Cammie. Not only is he having the best sex of his life with a woman so attractive he's stunned...