I've seen a few different versions of this story floating around on platforms like GoodNovel, but the core ending for the one I read, which I think is the most common serialized version, is pretty classic reconciliation. After all the back-and-forth, the ex-husband, usually named something like Adrian or Lucas, finally realizes the depth of his mistake and how much he took the female lead for granted. The big turning point is often him discovering some secret she kept, like an illness or that she secretly had his child after their divorce. The final act usually involves a grand, public gesture of apology, often during some high-society event where he humbles himself in front of everyone who once looked down on her. She resists for a bit, making him work for it, but ultimately accepts his renewed love. They remarry, and the epilogue fast-forwards to show them with their child, living happily. It’s a very wish-fulfillment ending, giving readers the satisfaction of seeing the cold, arrogant billionaire completely humbled and the wronged wife vindicated and elevated. The title 'Her Ex-Husband's Regret' is literally the entire plot arc summarized.
Some readers find it too predictable, but I think that's the point of the genre. You come for the catharsis, not for twists. The specific details that make or break it are in the execution—does his groveling feel earned, or is it rushed? In the version I finished, there was a subplot about her building a successful business after the divorce, which made her decision to take him back feel more like a choice of equals rather than her just being swept up again. The last scene I remember was them renewing their vows on a private island, with their toddler as the ring bearer. It wraps up all the emotional threads neatly, leaving no loose ends for the main couple, though sometimes a side character might get a hinted-at spin-off story.