I too enjoyed the exchange about hunters and Willoughby hunting.

I'm not a behavioral expert, but I am wondering it is true that he has a melancholy personality.

In ch. 3 we're told he's pleasing and gentleman like, diffident and shy, manners required intimacy to make them pleasing.

Marianne thinks he's a dud, but she also thinks a lover should have every taste coincide with her own. So maybe we should not believe her.

Elinor in Ch.4 told us he wasn't a dud.

Not until this week's chapters do we get to hear him speak for himself. He's no longer shy around the Dashwoods, so we get to see glimpses of his true personality. He seems funny and affectionate.

As to his melancholy and varying behavior during the visit, at this point in his life he has many reasons (some of them his own fault) to be depressed.

- He's waiting for his mother to make his fortune, he's dependent.
- He can't enter the profession he'd like because his mother probably throw him off if he did.
- He has foolishly engaged himself and is looking at spending his life with a woman he doesn't love (and perhaps he's seen glimpses of her ickiness by now)
- he can't have the woman he does love
- he should be beating himself up over leading Elinor on, while engaged to someone else.

He has a pretty bleak future ahead.
You could say that he could resist his mother and make his own way in the world. Someone like Captain Wentworth probably would have. But Edward's personality and situation are not like Wentworth's.