nprofile1qyt8wumn8ghj7un9d3shjtnyd968gmewwp6kytcqypqvadx9xpkfjxxgxhke8j93uuhd9k5enwlv7sgecr370flpf4dxgm6dpyx (nprofile…dpyx) When they do this in TV series I usually assume it's male writers/showrunners who identify with a particular character making sure that person gets the girl instead of the much better partner they temporarily had her with.
But we can't blame that here. But the author had probably pre-decided the outcome and didn't think about how interesting she was making the new fling & maybe that should change the story (or at least require stronger reasons for the planned choice by the character). And probably romantic tropes about going with the old reliable partner being better than the new & shiny. Or your perspective on what makes a good partner could just be different from hers.
(But again, I don't remember the books enough to have any opinion myself.)