The reason why Skylar had that look on his face when Chan-il told him about being introduced to Ri-in by Cirrus is because he realizes that Cirrus KNOWS he likes Chan-il. But in order for Cirrus to keep Skylar all to himself and keep Chan-il busy, he introduces him to Ri-in. If Chan-il is so pre-occupied with Ri-in, Skylar wouldn't have a chance to admire him more and would focus more on Cirrus. That's why he feels betrayed.
The reason why Skylar had that look on his face when Chan-il told him about being introduced to Ri-in by Cirrus is because he realizes that Cirrus KNOWS he likes Chan-il. But in order for Cirrus to keep Skylar all to himself and keep Chan-il busy, he introduces him to Ri-in. If Chan-il is so pre-occupied with Ri-in, Skylar wouldn't have a chance to admire him more and would focus more on Cirrus. That's why he feels betrayed.