Canonical romance is still a relatively new aspect of Doctor Who as a series. Sure, Tom Baker and Lalla Ward had some onscreen sparks that translated over from their offscreen romance, and more than a few fanfic writers might have some words about Pertwee’s Doctor and Delgado’s Master, but we didn’t legitimately see the Doctor fall for anyone on the show until Paul McGann’s Eighth Doctor kissed Daphne Ashbrook’s Grace in the 1996 TV movie. Since then the modern series has certainly had more fun with the gray area between friend and romantic partner when it comes to the companions — like Rose and, at times, Clara.
But then there’s River Song. The Doctor’s wife, the woman he would secretly tell his real name to. (Note: using male pronouns here since River has yet to encounter Jodie Whittaker’s Doctor in canon.) The woman the Twelfth Doctor would spend one 24 year night with at the singing towers of Darillium when the wind stands fair and the night is perfect, and he needed her the most. Introduced in "Silence in the Library," the character of River Song would be the first seeds of plot that incoming showrunner Steven Moffat would introduce, just prior to his full takeover. The bookend of that same plot was his intended departure episode from the series, with “Husbands of River Song,” before the BBC convinced him to stick around for one more season.
While the Doctor has flirtations and even the occasional flippant references to marriage, there’s something different about his relationship with River. As a character who moves through time in a non-linear way, it makes the most sense that the Doctor’s wife would be someone who experiences the universe in much the same way. Wandering on her own, with her own timeline detached from the Doctor’s, River has her own stories and adventures that aren’t locked entirely into his. The opening of journals whenever they run into each other to compare notes and determine where they are on each others’ timelines is the perfect detail of something that of course would be part of such a romance.
There are issues for sure. She begins as a fridged woman regardless of how her story unfolds in front of us as viewers, watching it from within the Doctor’s timeline. There’s a Schroedinger's Cat aspect to her, where she’s both living and killed off at the same time throughout her entire run as a character. This predetermined fate of hers can be a struggle sometimes, though there is the element of the fact that narratively she also looks at the span of her life from that very first story and makes the conscious decision for the Doctor not to change a moment of it.
A dark reflection of this is the opposite of this same aspect for River. Knowing that she’s met the Doctor after he already knew her, there’s a sadness to her understanding that one day she’s going to meet a version of him that is looking at her for the first time. We as viewers know this has already happened, and relating to River it feels very visceral and real, that feeling of no matter how in love we are with someone, we fear one day they’ll just stop, that they won’t see us in the same way anymore. With the Doctor, there’s a bittersweetness to it though. He doesn’t recognize her, doesn’t know he loves her, and yet he’s also intrigued by her. It’s like he instinctively knows she’s someone who he’s meant to be with. So while it could be read as someone not knowing you, it could also serve as that feeling of getting to fall in love with someone all over again.
The narrative supports this, as a matter of fact. “Husbands” is the very last televised River story, and according to her timeline, it’s the last time that she sees the Doctor prior to the events of the first time he sees her in “Library.” It’s also the furthest into the Doctor’s timeline that the two ever meet, which means that when she departs from him and then comes across him again, it creates the cycle all over again, so there is always a version of the Doctor meeting a version of River, on and on throughout time, and she’s always there waiting for him right before it ends for her.
There’s been a lot of speculation of whether or not River will return in the Chris Chibnall era to meet Jodie’s Doctor, but as much as I love the character, love the romance, and would love to see the two of them together at least once more, I also feel like it shouldn’t happen. The Doctor and River are so perfectly bookended with their repeating cycle from “Silence” to “Husbands” and back again, that to try to build or expand upon it now would risk cheapening it. Better instead for it to stand exactly as it does, a story held in time. Like the Doctor says to River at the start of their very, very long last night together, everything ends. And like the clanging of their wedding ring onto the metal floor of the TARDIS when Peter Capaldi’s Doctor finally regenerates, some things need to be let go.