
first thing. they are NOT in a relationship.
second thing. they've only met like once, twice.
third thing. he's a gangster. he knows the drug. going by his personality maybe he had quite no. of one night stands too and doesnt care much about matthew (for now). the feelings are NOT mutual yet. matthew may be naive, tender, sweet, patient (matthew best boy!) and entranced by him but Jin has a totally different persona from him. he probably has quite few things on his plate and that guy was an easy access presented just in front on him.
tag yourself im assistant wu