There's a stop she has to make, just her own, to a woman who has lived quite a long regeneration already. To the only person that she knows who might appreciate the totality of her fears.
"River," she says, knowing her at once. While the Doctor has a luxury of lives, she changes no more. Clara wonders, sometimes. She is cautious and brutal in ways her Doctor refuses to be. She's wearing that same military uniform that Clara keeps seeing her in the past few decades.
Clara hasn't quite figured out what River's doing when they're not around. Clara also suspects that there's a great deal she hasn't figured out yet.
River eyes her up and down. "Which one are you?" she asks, as she often does.
"Clara," she answers with a touch of sarcasm, although she's figured out by now that it's not the question that River's asking. "School teacher. 2010, Earth, Doctor with the bowtie."
River's expression brightens, beckoning her away from the TARDIS and the waiting Doctor.
They walk towards the edge of the cliff the TARDIS has landed them on, three suns setting in the distance. They stand together, staring out at a planet that Clara suspects has not had two living subjects on it in quite some time.
"What brings you here?" River asks. "What's he gone and done now?"
Clara laughs. "He hasn't done anything. Not exactly. There's a question I have, I think you can help me answer."
"Well, you've got my attention."
Clara grapples for where to start. Porridge. "...the man asked me to marry him. To rule with him. I told him yes. I barely know him, or what happens, or anything!"
"Well, what do you want to know?"
"You're married to the Doctor, so I think you're a bit of an authority on being married to men who rule the universe…"
River looks at her sharply, and Clara can almost see the realization in River's eyes. "I'm married to the man you love, too," she says, no judgment or malice in her voice or expression.
"Yes," Clara admits. "Which makes the matter that much more complicated."
"Does it?" River asks.
Clara closes her eyes, listening to a quiet breeze and feeling the dimming sunlight on her skin. "Will I be good enough if that's true? Will I always be… waiting for something that can't be mine?"
River laughs at this, deep and genuine. "Oh, I assure you that he can be and is. Clara, the Doctor has probably lived millions of years now. Sometimes he forgets, often he lies and assigns a number that he thinks humans can comprehend. He came before us, do you understand?"
"Yes, but…"
"Before fire and language and matter. Before your Big Bang. To try to confine a being like that into the incredibly selfish concept of loving only one thing… oh, silly girl," she says, pausing to breathe. "To even believe that he loves as we do! Your air loves each creature it gives breath to, certainly."
"I don't really understand how that changes things."
"I'm going to break one of my few rules and tell you something that you're going to figure out one day, Clara. You have more in common with the Doctor and I than you think. If you marry this Emperor, if you give your whole heart, might, your soul to him, for so long as he lives. Your whole life together will feel like a moment that ends too soon. One day you'll stand at the end of him, and the Doctor will still shine his light on you."
"What do you mean? How can that be true?"
"You'll need to live that part. But believe me when I say that the Doctor knows and will know you. If you're even considering this, then your Emperor is a man worthy of his own lifetime with you. You can be his own sun, if you want."
