The movie Indecent Proposal (1993) starring Robert Redford, Demi Moore, and Woody Harrelson ruined the ending of the book.
In the movie Indecent Proposal (1993), a billionaire proposes to sleep with the protagonist’s wife in exchange for $1 million, and the wife ends up having sex with the millionaire. A situation like this would be extremely damaging, leaving irreparable emotional scars. The couple fights, separates, but in the highly contrived ending, the wife returns to her husband, and they reconcile
In the ending of Jack Engelhard's novel Indecent Proposal, Joshua (who corresponds to John Gage, as the film changed the characters' names) refuses to reconcile with his wife Joan (Diana Murphy in the movie) and moves to Israel, since he is Jewish. This contrasts with the contrived ending of the film.
The movie could have offered a more realistic ending, with the couple ending up divorced. I understand they changed the ending for box office reasons, but it’s not plausible for the couple to stay together after what happened. The resentment would be immense.