I think James has drifted from any previous closeness he had with Catherine.
His priority is pleasing Isabella - he can't see much past her !
Isabella demands Catherine accompany them riding in the carriages. So, putty-like James insists Catherine agree to being frequently driven.
I think James has to contend with a selfish lover and the guy doesn't cope well. He wouldn't mean to distress Catherine yet he doesn't seem to realize he's doing so. He is weak, when it comes to falling in with the wishes of the Thorpes.
As James stayed with the Thorpes at Christmas, quite likely he's been under John's influence quite some time.

Cathrine has shown her integrity of her charecter and I think this has impresses HT. I'll be interested to see if brother James develops or learns from his mistakes in the course of the novel.

(pardon typos in post)

My impression is James has to contend with a selfish
I wonder how he changes in the story.

So far, he comes across as mild mannered and good natured like Catherine yet even more naive. To be sure, he's immersed in Isabella and I agree she'd be on better behaviour with James but gee, he is a few years older and we know he's been at university.
One would think he'sd have abit of experience !

I do get an impression he's known John since being at Oxford, or at least since hisearly days.
John may've been there a term or two longer. He brags of his parties, no doubt to impress. Possibly, he invited freshman James who is now under Thorpe's influence.

Well, that's one take ! :)