A Marrying Man by G.B. Stern

For two days Teddy made Kathleen conspicuous by his gallant attentions; so that on the evening of the third day she was somewhat taken aback when, instead of inviting her to sally forth for their usual stroll round the Capstone, he merely lingered in the hall after dinner to gladden her by a little airy chat, and then rather abruptly disappeared. A rumour passed about, later on, that he had been seen acting escort to a young girl, a very young girl -- only his senior by four years or so.

Kathleen understood that she had been wrung dry of all material necessary for yet another addition to his "Observations of Eve"; and that now he was allowing himself a little pleasant relaxation from conscientious psychology. He was young enough, and she old enough, that without embarrassment she could sham extreme indignation and a broken heart to those who chaffed her on his desertion. But she was sensible of a slight feeling of mortification, nevertheless; it was not in the nature of Kathleen to take even a schoolboy's defalcation lightly. She determined, however, to let no trace of this appear in her manner towards the culprit, when he should choose to approach her with a contrite desire to renew their charming intimacy. She was reading in the sitting-room the following morning, when Teddy marched in -- and, on seeing her, looked very much inclined to back out again, speedily.