Delia Leon is Dixie's younger sister whom he is strongly protective of. This includes showing distaste towards any guys, including Linley, who his sister requests from him to protect while in the Magical Beast ranges.
Dixie knows little of Linley. As of Chapter 34, they are both in the Mountain Range of Magical Beasts. Despite his fierce protectiveness over his sister, he is not without without a sense of respect, acknowledging that Linley's decision-making skills would be worth supervising during his individual journeys in the dangerous mountain terrain. (This information is from the manga/manhwa).