"Presenting Trilby Swain", a short story by Ron Goulart, first published in The Magazine of Fantasy and Science Fiction, May 1981, available at the Internet Archive.
The sad and bizarre story of a man who shared his wife with
2,000 other men, presented by Ron Goulart [. . .]
The story revolves around an unemployed and jealous husband and his famous and beautiful wife. [. . .] thousands of androids who look just like her are created for their admirers to love.
How would you feel if 2000 men were screwing your wife?
[. . .]
Right this minute, Doug scribbled, maybe 40 guys are in the sack with her!
[. . .]
Sighing, I wrote, You shouldn't believe Pinajian's figures. According to Fax Variety there are only 1846 Trilby Swain Lovebots in circ—
1846 or 2000! What does it matter? His pentip dug deep into the plyocloth. How would you feel if even only 1846 bastards were thrusting their misshapen members into your wife's—
I recall the husband in a flying automobile being prompted to drop his wife into the void because he is inclined to think she was an android.
"You're not Trilby," he told her evenly. "I know my wife, and her you ain't. You look like her, talk like her, think like her and still you are not Trilby."
She pressed her warm fingertips to his cheek. "Doug, you really are acting—"
"If I dropped you from this height, we'd prove it quick. You'd make a nice nutzenbolts smash when you hit the ground. I may just try that test."
At the end of the story, he suspects she is having an affair with the man responsible for the droids' creation, and after catching them in a hotel, he kills the man and his wife, only to discover she is an android. The police find him nonstop laughing.
He stood there, with Pinajian's dead body sprawled at his feet and the ruined android toppled against him and splashing him with oil.
"It isn't Trilby. It's an android."
That was true. Trilby had been seeing Dr. Kanzoo those afternoons, mostly because she was so upset about what had been happening to her and Doug. She'd been afraid to tell him where she was really going.
Doug, the kilgun still clutched tight in his fist, moved a pace back and the lovebot fell to the floor.
"She's faithful," he said. "She wasn't here. She's been absolutely faithful."
He started to laugh. And he never stopped.