This article contains major spoilers from Harry Potter and the Cursed Child, and is meant to be read by people who have seen the play or read the script book, and are ready to talk about it. If that's not you, read on at your own risk! (For a spoiler-free reaction to the play, check out this article.)
With Harry Potter and the Cursed Child, J.K. Rowling and Jack Thorne not only had the opportunity to bring us further into the Potter universe to see what becomes of the next generation, but also delve into the past, where mild-to-massive chaos ensues in various timelines. In the process, more than a few what-if scenarios occurred, including some that involve the relationship between Ron and Hermione, posing a pretty major question...
Are Ron and Hermione really meant to be together?
It's a question that's especially relevant for those who recall that interview between J.K. Rowling and Emma Watson a couple years back, in which the two pondered the romantic future of Ron and Hermione. As a fan of the series, this is one of the topics that stood out to me when I saw Cursed Child, and it's one that I kept in mind during my read-through of the script book.
Cursed Child's answer is actually pretty complicated, as the time-turner shenanigans expose just how fragile their romance was to begin with. To recap, Scorpius and Albus were attempting to stop Cedric Diggory from completing the first Tri-Wizard by posing as Durmstrang Students. During this attempt, they encountered Hermione, who's naturally a bit suspicious of their behavior, when they spoke to her without accents. Upon return from their failed attempt to thwart Cedric, the two boys find reality mostly the same, only Ron and Hermione are not married, and Rose and Hugo no longer exist. Hermione appears to be single, and working as the Defense Against the Dark Arts professor at Hogwarts. She also seems to be in a perpetual bad mood, possibly because she has no goofy husband to inspire her to loosen up now and then. Also living in relative misery is Ron, who's uncomfortably married to Padma (Patil). They have a son that Ron can't seem to stand, and Ron's fun, lightheartedness appears to have been replaced with tension and dismay.
So, what happened? Why aren't Ron and Hermione together anymore? Turns out, Hermione didn't go to the ball with Viktor Krum, due to her wariness of the Durmstrang students she saw during the first task. Instead, she went with Ron. They had a fine time, but Ron enjoyed himself a bit more with Padma, and ended up dating her. He and Hermione resumed friendship, and nothing more came out of it.
Does this mean that the key to Ron and Hermione's whole relationship was the Yule Ball in their fourth year? Because that one event played out differently, does that mean their whole relationship is null and void? Well, kind of, but it's a bit more complicated than that, as evidenced by their behavior in the new timeline, and the one that follows.
In the real timeline, Hermione went to the Yule Ball with Viktor. They had a blast, but the night was ruined by Ron, who went with Padma, spent the whole night sulking over Hermione and Viktor, and later made Hermione feel bad about it, leaving her angry and in tears. One would hardly call that the start of a budding romance. And we know the two didn't actually get together until years later, so it's not even as if they began dating as a result of the fight. But the argument (or the jealousy that prompted it) does seem to be the spark that ignited their attraction to one another, whether they realized it or not at the time. It's a spark that Scorpius and Albus attempted to recreate with the fireworks display during the second task (the second time they go back in time). It doesn't work. In the new, far darker reality, Hermione and Ron are working together to fight Voldemort, but they are not romantic. Their friendship lasted, even after Harry died, but they never actually got together.
When considering this question, it needs to be pointed out that there's evidence in the alternate timelines that there was and will always be something between Ron and Hermione. Looking at the post-first-task timeline, Ron and Hermione are separated and unhappy, but we do see some flickers of interest between the two of them when they cross paths at Hogwarts. And their affection for one another is put to the test in the darkest timeline, when the Dementors are pursuing them. Ron is injured, and maybe he wasn't going to get far if he tried to run, but he still chose to stand by Hermione's side and face certain soul-sucking death at the hands (and kiss) of the dementors, than to abandon her.
Hermione: A daughter.
Ron: And a son. I liked that idea too.
He looks around -- he knows his fate.
Hermione: Kiss me.
Even in realities where Hermione and Ron are not married, there is still a connection, and maybe even a vague romantic awareness of one another. But in reality -- the one that sticks -- not only are they married, with children, but they really are in love. She's a serious and successful Minister for Magic. He's kind of a goofball dad, pranking people and working at the joke shop. But there's evident love and chemistry between them. Enough so that Ron wants to renew their vows... soberly, this time.
Their relationship may not be a true storybook romance, but it's very clearly rooted in friendship and mutual attraction. And it all seems to hinge on a spark between two young teenagers. Or, to borrow a phrase from Scorpius, Ron's Yule Ball jealousy and the fight that ensued after seems to have been the acorn that would grow into their eventual marriage.
As for anyone still questioning whether Harry and Hermione might've been better off together. I suppose that question's still going to be out there, as the play doesn't really acknowledge the prospect. In Harry Potter and the Cursed Child, at most, they're work-married. At the Ministry, they behave like two people who've been friends for most of their lives. He's supportive and comfortably familiar with her. She's on him about staying on top of his paperwork. They get each other. If there's any kind of chemistry between them beyond that, it's not present in Cursed Child. If anything, the play goes out of its way to demonstrate that there will always be something between Ron and Hermione, whether they're together or not. And of the timelines we saw, they're clearly happiest with each other than they are apart.