When Adelyn confessed, he was a little shocked because he never excepted her to fall in love with him so easily, and for her to tell him of her feelings without hesitation. He did not have feelings for her during that time and was not ready to even think about marriage, which was why he rejected her.
He thought she would cry or fuss about it, but it surprised him when she said nothing. It bruised his ego that she might not have real feelings for him that's why she just gave up, and the next time they met, she just pretended as if nothing happened.
