How did the affair between Felix and Charis begin?

The affair between Felix and Charis began the previous summer when Felix and Charis become friends, and they often talk by the pond. One day Felix kisses Charis. Both are shocked, and Felix immediately apologizes. They get over their embarrassment in the coming days, but the feelings remain and the flirting escalates. One day Felix develops a plan for the two of them to go away and stay at a hotel posing as husband and wife