She worries that they are too alike.
"We could never be together because of the similarities" and as soon as she has said it she knows that it was a mistake.
This is the difference between them. She sees their love of Art and literature, he notices her anxiousness and vaguely contained fury. To her they are too close. To him they are too far apart.
She sees a film at the cinema and knows that he would like it too. She recommend it. He downloads it and shrugs telling her that it is okay.
They make love and she is struck by her inability to feel intimate, even when she is completely naked before him. He tells her that this time was the best ever.
They have strayed past the end of the thing. Somewhere, without a finishing line to snap with her out-pressed chest they have run the course to its completion. No one to pat them on the back or bring them post race refreshments and so together they keep running, stopping now and then to look back at the ever-lengthening distance behind them, wondering if it is up to them to shake hands and, exhausted, walk off the track.
Damp-eyed she hugs him goodbye knowing that it is for the last time. Cheerily he kisses her on the cheek and tells her that he'll see her next week. When he is gone she stands on the track and bends at the waist and breathes till the pain lessens. She could just walk away. Should. Will.
She spends a day in mourning, crying for a thing that is now lost.
He calls. He sets a time and a place and at some point in the conversation he makes her laugh. She picks herself up off the grass and performs a few half-hearted stretches. Slowly at first, but with increasing vigor, she begins to run again.