Well, Matthias will just have to be extra charming to ensure he gets to see just a few of Seong's warning glances at would-be suitors. It does so charm him when Seong's possessive. Does he realize there's no danger of Matthias picking another over him (at present)? Maybe there is. He did tell Seong the day they officially met that he's walk away from whomever he was with at the time for him. In his defense, Matthias was already halfway out that door.

"I guess you'll just have to stay very close, then, hm?"