This is the short story "Hunters in the Forest" by Robert Silverberg, originally published in the October 1991 issue of Omni (it's currently available in his time travel themed short story collection Time and Time Again). Here are the first two paragraphs describing the trip to the Cretaceous with three options for travelers:
Twenty minutes into the voyage nothing more startling than a dragonfly the size of a hawk has come into view, fluttering for an eye-blink moment in front of the timemobile window and darting away, and Mallory decides it’s time to exercise Option Two: abandon the secure cozy comforts of the timemobile capsule, take his chances on foot out there in the steamy mists, a futuristic pygmy roaming virtually unprotected among the dinosaurs of this fragrant Late Cretaceous forest. That has been his plan all along—to offer himself up to the available dangers of this place, to experience the thrill of the hunt without ever quite being sure whether he was the hunter or the hunted.
Option One is to sit tight inside the timemobile capsule for the full duration of the trip—he has signed up for twelve hours—and watch the passing show, if any, through the invulnerable window. Very safe, yes. But self-defeating, also, if you have come here for the sake of tasting a little excitement for once in your life. Option Three, the one nobody ever talks about except in whispers and which perhaps despite all rumors to the contrary no one has actually ever elected, is self-defeating in a different way: simply walk off into the forest and never look back. After a prearranged period, usually twelve hours, never more than twenty-four, the capsule will return to its starting point in the 23rd century whether or not you’re aboard.
I'll quote the other parts you described too, though as you say they are spoilers, and if you want to re-read it you'll probably have more fun reading it straight through.
Here's the conversation with the woman he meets in the Cretaceous, where she says she took Option Three:
“How long have you been here?”
“About a week. Maybe two. I’ve lost count, really. Look, there are those ankylosaurs I was telling you about.”
He ignores her pointing hand. “Wait a second. The longest available time tour lasts only—”
“I’m Option Three,” she says.
She tries to convince him to stay:
“Stay here with me!” she says. “Let your capsule go home without you, the way I did.”
“But the dangers—” he hears himself blurting inanely.
“Don’t worry about them. I’m doing all right so far, aren’t I? We can manage. We’ll build a cabin. Plant fruits and vegetables. Catch lizards in traps. Hunt the dinos. They’re so dumb they just stand there and let you shoot them. The laser charges won’t ever run out. You and me, me and you, all alone in the Mesozoic! Like Adam and Eve, we’ll be. The Adam and Eve of the Late Cretaceous. And they can all go to hell back there in 2281.”
But he does return, and here's the ending section at the party:
In mid-October, seven weeks after his return, he is telling the somewhat edited version of his adventure at a party for the fifteenth time that month when a woman to his left says, “There’s someone in the other room who’s just came back from the dinosaur tour too.”
“Really,” says Mallory, without enthusiasm.
“You and she would love to compare notes, I’ll bet. Wait, and I’ll get her. Jayne! Jayne, come in here for a moment!”
Mallory gasps. Color floods his face. His mind swirls in bewilderment and chagrin. Her eyes are as sparkling and alert as ever, her hair is a golden cloud.
“But you told me—”
“Yes,” she says. “I did, didn’t I?”
“Your capsule—you said it had gone back—”
“It was just on the far side of the ankylosaurs, behind the horsetails. I got to the Cretaceous about eight hours before you did. I had signed up for a 24-hour tour.”
“And you let me believe—”
“Yes. So I did.” She grins at him and says softly, “It was a lovely fantasy, don’t you think?”
He comes close to her and gives her a cold, hard stare. “What would you have done if I had let my capsule go back without me and stranded myself there for the sake of your lovely fantasy? Or didn’t you stop to think about that?”
“I don’t know,” she tells him. “I just don’t know.” And she laughs.
