Guthrie sleeps with Judy

Guthrie sleeps with Judy. Perhaps Haruf included it as to not take away from the intimacy between Guthrie and Maggie by letting us know that he has had a vasectomy. Why is this important? He and Ella decided that they didn't want any more children. Maggie is upset that Guthrie has slept with Judy. Cigarettes are abundant.