In an interview given over the weekend, J.K. Rowling admitted that Ron Weasly and Hermione Granger do not belong together. According to EW, Rowling put them together as wish fulfillment.
“I wrote the Hermione/Ron relationship as a form of wish fulfillment,” Rowling said. “That’s how it was conceived, really. For reasons that have very little to do with literature and far more to do with me clinging to the plot as I first imagined it, Hermione ended up with Ron.”

This is what we love about fiction. Ten years on, Ron and Hermione are and will remain together at the end of the Harry Potter series, and there is nothing any one can do to alter this. Even the great and powerful author herself.* Because stories, upon their publication, are no longer in the hands of their makers. They are the now occupants of the individual imaginations of those of us who read them.
The creation is unleashed at publication, at which point the writer (or director or actor, etc) no longer has any more say on story than those of use who read it. That J.K. Rowling does not wish Hermione and Ron to have ended up together is interesting, and I’m glad to have her opinion on the matter. But, really, her opinion on the conclusion is just one among millions.
As for me and my house, we shall continue being happy about the Granger-Weasley pairing. A little romantic catharsis is good for the soul, given the hard work setting the characters in motion has been accomplished. And, Ms. Rowling, fear not. The messy disastrous emotional muck of a budding young adult relationship was more than built in the thousands of pages you gave these two kids. The pay-off is welcome, even if it’s lessened by that 19 years later bit.
*Barring a sequel in which the two are involved in a divorce, but Rowling wouldn’t do that to the kids, right?