Ms. Schreiber, 41, is the daughter of James Schreiber, a well-known Greenwich, Conn., lawyer and investor, and a sister of Zachary Schreiber, the chief executive of PointState Capital, a $5 billion hedge fund. Ms. Schreiber, an American civilization graduate of Brown University who runs a Rolfing massage practice in Los Angeles, met Mr. Patric in 2002 when he went to her as a massage client and the two became a couple, dating off and on for a decade.

She had long wanted to be a mother, according to a family member. But pregnancy attempts with Mr. Patric did not go well. “I even had a surgery to increase our chances,” he said in an interview last week.

They decided in 2009 (at a time when they were not romantically involved but still friendly) to pursue artificial insemination. Ms. Schreiber, who declined an interview request for this article, was keenly familiar with fertility options: Her mother, Linda, had become a bit of a celebrity in her own right in the 1970s after a regimen of the pregnancy drug Pergonal resulted in quadruplets. (Ms. Schreiber is one of them.)

Along came Gus, named after Ms. Schreiber’s paternal grandfather. The boy’s middle name is Theodore, a nod to Mr. Patric’s family heritage.

The baby eventually helped rekindle a romance between Ms. Schreiber and Mr. Patric, although they never formally moved in together. For the next two years, Mr. Patric said that he played a parental role (“I took him to get circumcised when he was 8 days old”) and that Gus, now 4, referred to him as “Dada” in videos and messages. “Thank you for teaching me to pee in the toilet, watch airplanes, learn Beatles songs. I love you Dada, Gus,” read a card that was written by Ms. Schreiber, given to Mr. Patric and later presented as evidence in court. (A lawyer for Ms. Schreiber contended that Mr. Patric did not attend the circumcision, but did provide a ride because she could not drive after a cesarean section.)

Then, in June 2012, the couple broke up for good. Shortly thereafter, Mr. Patric filed a paternity suit for shared custody. According to both sides, there was legal mediation, during which time Gus continued to see Mr. Patric.