I'm not entirely sure that Clark was really attracted to Mayson. More like he was flattered by her interest in him. I think he appreciated that she was a strong, independent woman (that's clearly his type), and was curious about her opinions on Superman, and I bet a tiny, petulant part of him liked knowing that her attention was making Lois jealous. I do absolutely believe his grief at her death - the tragic loss of someone who could have become a very good friend. I also think that you're right in this story that he would have felt guilty about unintentionally leading her on - that he should have been more honest and firm about his lack of romantic interest. Chalk that up to his limited experience with women.
