"You're my pack now, Su-jin. You'd have to try very, very hard to get rid of me."

Because it took something major to cause someone to be able to break the bond a pack had. True it wasn't typical for a pack to include those who weren't wolves in it but it wasn't completely unheard of. After all, packs were known to do what his did and adopt outside races. In the end he'd become a wolf himself but he knew that wasn't an option for Su-jin and that was alright. He was happy to have him as he was.