Middle life crisis hits too hard on this poor man. This is why you shouldn't listen to cheater's advice. It's not daddy's fault that communication or any kind of depth in the intimacy never happened, the sugar is too underdeveloped for any mature conversation to happen.
Sihoon is a quiter, and definitely have hard time opening up but there are clear progress in their development. Junyoung... boy.... always a boy, no wonder you're besties with mari