The Amber Liquid

That night, Belle and Arthur returned before Stefan could leave. At first, Trixie was dreading the moment that her brother would find Stefan at his house with her, and the fact that it was Arthur who sent Stefan didn't help.

She could still clearly remember Arthur's disfavor of Stefan being Trixie's friend. She cannot blame him. Stefan's reputation for changing girlfriends weekly is very well known. Everyone would raise a brow at her and Stefan's relationship and would think that it wouldn't take long before she would be included in Stefan's long list of girlfriends.

It is not a secret that Stefan's relationship was purely in bed and he didn't hold any romantic affection towards those women. That didn't stop Trixie's growing affection for him.

So Arthur has every reason for disallowing Trixie to be friends with Stefan.