What are the poet’s thoughts and feelings in the last stanza? How are these thoughts and feelings conveyed?

    Only when the train heaved noisily, only
when it jolted, when it slid away, only then,
daring and secure, she smiled back at my smile,
and I, daring and secure, waved back at her waving.
And so it was, all the way down the hurrying platform
as the train gathered atrocious speed
towards Oxfordshire or Gloucestershire.