Chained

He is chained to her through his own choice.

She is chained to him through no choice of her own.
A thick chain linking the two of them together by their ankles and kept in place with heavy-duty locks.
She knows why she is there. He has explained that once - and only once. Each subsequent time she asks, he simply tells her that she knows the reason. She knows there is no way out until he says so.

For a time of his choosing, she is his prisoner and that is all there is to it. Yet - for the two of them - things could have been so, so different.