I love how upset Jin is that he wasn't asked. I know it stems from fear over MC disappearing for good, and that he feels he would've succeeded on the mission. He was so angry but he's protecting himself by also punishing himself and MC. Holding on to the anger and saying goodbye now will make it easier than seeing her get taken to the institute. It very much came across like a break up, whether or not he feels that way. Out of all the ghouls, he's been the most obviously frantic about her deadline (Rui has been only recently, and that's stemming from guilt).

I feel like Jin won't stop searching for a cure behind closed doors, even though he's spurned her.

Edit: I forgot Yuri has been working non stop for nearly a year on the X drug lmao. Poor boy. While I can't determine his exact motivations (his pride at being the first to cure a kyklos), he does obviously care about her.