Honestly I think they were both very very unhappy in the marriage, and it was a huge mistake. They both will have felt trapped. As said, i think they had three dates before they got engaged, they barely knew each other, it was more like an audition to fill a position than falling in love and getting married,
It’s weird in hindsight, we all watched that wedding, the sort of “fairytale” story line, and although it was acknowledged she was young, we really all should have been saying. “ fuck me, she’s a teenager he’s only met three times,what’s happening here then”. But most folks bought into the fairy tale and didn’t question it too hard. It also wasn’t really known they didn’t really know each other at all before they got engaged and had barely met.
He married as he needed to find a suitable virgin and have kids, the heir and spare. She married as she was a starry eyed teen excited over what was involved, future queen, living a life of huge privilege etc. Possibly even romanticised how he’d fall in love with her.
It could have worked, they could have had their kids and quietly had their discreet affairs, both living independent lives, co parenting and getting together for social events, but it got to the stage they couldn’t tolerate each other.
Overall it’s a very sad situation.