“I’m not a bad guy,” Junot Diaz writes to begin his short story collection,“This Is How You Lose Her.” From there, the Pulitzer Prize-winning author jumps into nine vignettes that revolve around love.

The stories mostly focus on Yunior and his brother, Rafa, young immigrants who came to America from the Dominican Republic. They callously womanize their way around, but just as the book threatens to deteriorate into a swaggering recollection of past sexual encounters mixed with much-deserved heartbreak, Diaz suddenly shifts gears.

Romantic love takes a backseat to the familial variety as Rafa slowly and bitterly succumbs to cancer. Yunior flashes back to memories of his father, a frightening man who brought his sons to the openness of the United States only to confine them to their bedrooms.

The book’s highlight is a short story previously published in The New Yorker, related to Yunior only thematically; “Otravida, Otravez” seems to span a woman’s entire life. Using a female narrator, Diaz advises girls recently arrived in the United States, a country that offers the quintessential social dream but forces them to sever familial bonds. It’s the complications that bring out the tenderness, and by the time Yunior starts whining about his broken heart again, the reader understands his environment well enough to sympathize.

Diaz draws together the meandering short stories by zeroing in on the voice of a Latin-American immigrant. His energetic second-person sentences are filled with Spanish and profanity. The lowbrow diction feels honest and powerful, but occasionally grows tiresome.

Several of the long dialogues are built with banalities, and Diaz sometimes strains too obviously for colloquial eloquence. One passage reads, “The daughter doesn’t seem to understand what’s happening but when the door shuts she lets out a wail that coils around you like constantine wire.” He’s referring to the loops of razor wire used on top of prison walls, and though the metaphor does evoke the neighborhood, it’s wrong for this narrator and for the cry of a child.

The wonderful moments shine, but since Diaz is a master writer who based Yunior largely on his own experiences as an immigrant from the Dominican Republic, he has little excuse to let the short stories fall flat.

“This Is How You Lose Her” by Junot Diaz released worldwide on Sept. 11.

A version of this article appeared in the Thursday, Sept. 13 print edition. Leora Rosenberg is a contributing writer. Email her at [email protected]