Cheated
It turns out Heather and the man she met at this fair had been in a relationship for a year. Both John and the other man had been duped; neither had any knowledge of the other. Both men were unaware that their girlfriend was in a relationship with another man.
This was a major disappointment for John. He had a prosperous future and was completely in love with Heather. John never saw the unidentified man again after he stormed out of the room. John demanded indignantly that Heather leave. She did so, leaving John in the room alone.