You have touched on one of the excellent elements of this short story. It is clear that Hemmingway, in choosing to tell the story, remains very distant from the dialogue and action. This story has a large amount of dialogue with very little input from the omniscient narrator - it is as if he is choosing to deliberately distance himself, not commenting or judging. It is clearly left up to the reader to make any judgements as we eavesdrop in on this conversation and piece together what is happening.
However, having said this, I think the reader feels more sympathy for the girl than for the man. Note the insistence with which he keeps on making her consider the abortion, and in the end, note how she responds:
"Would you please please please please please please please please stop talking?"
It is clear that she feels pushed into a corner and has to decide between keeping the relationship or keeping her child. Reading between the lines reveals the pressure that the man is placing her under and the impossible position the girl is in.