One of my biggest disappointments/hopes for the future is that we never got to know what Jason thought when he saw the Case in the cave, when he came in to hear Bruce's message. Way to tease, DC. Please don't feel obligated to reveal how he felt until you find a writer who can express it in as heartbreakingly perfect a way as the above scans.
It's a twist on the "who do you save" situation.
Yeah. In a certain way, it's also an Oedipian scene; the subtext has always been there in shades, but Under the Hood plays a lot with it. Earlier in the arc, Joker says that "comedy is best in threes. Like Batman, Robin and me", to which Jason absently replies, "yeah, we're one big happy family". The link between Joker and Jason's mother, of course, goes without saying. Jason takes Joker's old identity to goad Batman. I don't know if Jason's aware of Joker being the symbol Bruce puts on not crossing the line, but he's trying to get to being Bruce's most important thing. (It's worth noting that the previous issue ended with Blüdhaven exploding and Jason managing in getting Bruce to stay rather than flying off to check on Dick, so that was a win - but only because Jason told Bruce Joker was going to die if Bruce left, so that wasn't.)
Or more likely, he's proving to *himself* that Bruce never really loved him. Exactly. I can't imagine Jason didn't know on some level that he was setting himself up to fail. There was no way Bruce was going to cross the line, and if Jason really thought he would - well, then he's a lot more delusional/fucked-up/in love (and I mean filial love just as easily as romantic love) than he generally manages to act.