The first thing you need to understand about Polly is that she goes out of her way to draw the attention of the boarders, with the intention of choosing one who might make her a suitable husband. Mr. Doran soon becomes the object of her intentions. She is an attractive girl, described as "slim" with "light soft hair" and a "small full mouth." Her physical appearance certainly has nothing to do with why Mr. Doran does not want to marry Polly.

Perhaps the most telling description of her appearance, however, is that her mannerisms make her reminiscent of a "perverse little madonna." This is an introduction to Polly's vulgarity, which forms part of the reason why Mr. Doran does not want to marry her.

It transpires that Polly and Mr. Doran have slept together and that Polly is pregnant. The first reason that Mr. Doran does not want to marry Polly, or have the affair made known at all, is that he is worried about his career. He is deeply concerned that all his years of work may go to waste if what he has done becomes common knowledge.

I would argue that the main reason Mr. Doran does not want to marry Polly is that he considers her to be beneath him. He thinks about Polly's "disreputable father" and about her mother's boarding house, which is starting to get a colorful reputation. In addition, he considers Polly a little vulgar and notes that she does not always speak properly.

While Mr. Doran cannot decide whether he likes Polly or hates her for what she has done, it is very clear to him that he does not love her, and his instinct is to stay "free" in spite of what has happened. While he longs to run away, he is painfully aware of the ramifications of what he has done.