The story you described is "Chance", a novelette by Connie Willis, first published in Isaac Asimov's Science Fiction Magazine, May 1986, available at the Internet Archive. The story (tagged "fantasy" at the ISFDB) is about an unhappily married woman whose creep of a husband is hired by her old alma mater, and she seems to experience or hallucinate a kind of timeslip.
Editorial blurb:
Sometimes life seems to go round in circles, events repeating themselves endlessly. Yet we can't go back to the moment when our roads divided, and to when we, perhaps, set off down the wrong
path.
Elizabeth has come back to her alma mater:
"No, I can't stay. I know you're trying to get unpacked. I'm sorry you had to move in in all this rain. We usually have beautiful weather here in the fall." She smiled at Elizabeth. "Why am I telling you that? Your husband told me you went to school here. At the university."
"It wasn't a university back then. It was a state college."
"Oh, right. Has the campus changed a lot?"
Elizabeth went over and looked at the thermostat. It showed the temperature as sixty-eight, but it felt colder. She turned it up to seventy-five. "No," she said. "It's just the same."
She meets her younger self in a (hallucinatory?) timeslip:
The girl who had been Elizabeth Wilson put her books down on the cement bench and came and knelt down by Elizabeth. "I hope we don't collapse in a heap," she said, and smiled at Elizabeth. She was a pretty girl. I didn't know that either, Elizabeth thought, even when Tupper told me. She took hold of Elizabeth's arm and Tib took hold of the other.
"Tripping innocent passersby again, I see. How many times have I told you not to do that?" And here, finally, was Tupper. He laid his bike flat in the grass and put his bag of Tupperware beside it.
Tib and the girl that had been herself let go and stepped back, and he knelt beside her. "They're not bad girls, really. They just like to play practical jokes. But banana peels is going too far, girls," he said, so close she could feel his warm breath on her cheek. She turned to look at him, suddenly afraid that he would be different, too, but it was only Tupper, who she had loved all these years. He put his arm around her. "Now just put your arm around my neck, sweetheart. That's right. Elizabeth, come over here and atone for your sins by helping this pretty lady up."
If this is the right story, that leaves us with the problem of finding the collection you read it in. It has appeared in several compilations of science fiction and fantasy. Given that you read it about twenty years ago, maybe it was Willis's 1994 collection Impossible Things or her 2007 collection The Winds of Marble Arch and Other Stories. These collections can be borrowed (for free but registration required) from the Internet Archive: Things Winds
