First Henry asks Cathrine to dance, but she is waiting for John Thorpe. At the next ball he has the opportunity to dance with her, however during the begging of the dance she takes time to talk to John Thorpe. Third Henry expects to take a country walk with Catherine and she stands him up to ride around with John Thorpe. Which brings us to this moment when he sees her in the theatre and comes to speak with her, she is sitting in the box with John Thorpe.

Henry is most likely dealing with a flurry of emotions here. For one, Henry being a very cleaver individual could presumably see through the artifice of JT and must be a little disappointed that Catherine would choose him as a companion. At the same time he is frustrated as every time he seeks to further his acquaintance with Catherine, John is standing in the way. And finally he is jealous and concerned that Catherine desires John's company more than his own.