Comment by haku on Shutline - Chapter 55

At the begging Jake was upset because he saw the bite marks on Shin and thought he slept with the other guy and Shin assured him that he didn't, and that he punched him instead.

In the car when Jake mentions Gren getting caught and now they know what he looks like he's basically been marked so depending on what Gren decides to do with his future, Jake can't protect him anymore. And shin is excepting that, and saying that Gren is an adult, so what he does is up to him, and that he understands that there's nothing he can really do. 

At the end Shin is just saying that he is already aware that he is tied up with Jake and that he's already excepted it (cut to him telling Jake that  basically if he goes down, he's going down to aka thought they ar in it together) 

thank you my love for explaining to me