Katie was getting upset that Mike was acting and speaking as if he wanted her to marry Henry. I didn't hear the whole speech she gave, but basically she was regretting/re thinking the whole plan. Henry just sort of just shut down and started towards the door of the cabin. Katie asked where he was going and he said to check the air pressure in his tires. He walked out, shut the door and sat on the front step and put his head in his hands and started to cry. Katie was puzzled by his answer and went to the door and looked out to see him crying and it was as if a lightbulb came on. She finally understood that Henry really loves her and wants to marry her. Of course she feels rotten and tells Margo she is a selfish jerk and has ruined her life and Mike's and Henry's.
anyone else feel free to fill in any of the blanks i left.