John Kenrick did a pretty detailed analysis of fact vs. fiction in FUNNY GIRL.
https://www.musicals101.com/brice.htmAmong the many interesting bits about Nick Arnstein.
"Both the play and movie were produced by Fanny Brice's son in law, Ray Stark, who had the unenviable task of appeasing Fanny's surviving family and associates -- including Nick Arnstein. With Nick only too eager to initiate a lawsuit, Stark had to reshape history. And as Nick's character was fictionalized, other aspects of the story had to change too."
"Nick Arnstein "gorgeous"? Oy vey! Compared to who William Howard Taft? He may have been sophisticated, and at 6'6" he towered over most men, but he was not a beauty."
"Funny Girl depicts Arnstein as a classy gambler who turned to crime because he didn't want to live on Fanny's money. Not so! Nick was a common criminal and had no qualms about sponging off Fanny for their entire marriage. Before meeting her, he had already been arrested for swindling in three European countries. Shortly after they met (and before their marriage), he was jailed for wiretapping. The lovesick Fanny visited him weekly in Sing Sing, so she knew what he was long before they exchanged vows."