I interpreted Matthew’s smile as a delusion Jin was having in the moment because of the drugs. It’s sad. Jin is possessive of Matthew’s smile and the fact that he is relapsing because of the drugs and is hallucinating/remembering his past is making Jin spiral out of control. Matthew tried to keep Jin safe in his own way. I honestly believe he was trying to prevent the relapse to do further damage and make Jin addicted again. I could be wrong but again that’s how I interpreted it.
That military flash back got me breathing heavily.
Lol. Yes