I think it's about Gretta's thoughts after breaking up the long relationship with Dave and she's thinking about moving on and leaving all those memories behind. Maybe it's about the moment after she leaving Dave's place and carries all her stuffs waiting for the train and thinking what about to do next because if she chose to leave maybe there'd never be a chance to come back again like stepping on the train with one-way ticket.
I think it's about Gretta's thoughts after breaking up the long relationship with Dave and she's thinking about moving on and leaving all those memories behind. Maybe it's about the moment after she leaving Dave's place and carries all her stuffs waiting for the train and thinking what about to do next because if she chose to leave maybe there'd never be a chance to come back again like stepping on the train with one-way ticket.