I do think he is/was genuinely hurt by Kim dropping the "I'm gonna go to S&C as a partner" idea.
The way I kinda looked at it was that everything leading up to that moment has been him kinda-sorta struggling with the Chuck dying thing. He certainly resents the shit that Chuck did, and wanted him to get some comeuppance, but not dying like that. When he dropped the "WELP, THAT'S YOUR CROSS TO BEAR!" at Howard, I feel that was his way of trying to pass the buck and feel less terrible about it. But, it didn't really work. He wanted to be a lawyer to impress his brother. He worked REALLY hard. Seeing him slip away into the law library in the cold open after playing verbal grab-ass with Kim, only to have Chuck kinda give her a little shine from her knowledge in certain case law, was indicative of him sort of wanting to impress/earn the respect of Chuck.
When he got the call from the executor of Mrs. Strauss' will, he was visibly upset (and had no real reason to fake it, as he enjoyed that aspect of law, he got a little bit of respect from Chuck for having done well with it). He even still referred the dude to HHM to throw them a bone, even though he easily could have done the same for D&M. Then, his last real hope of being lawyerly was with Kim. But she doesn't want to be pigeon-holed as strictly banking (the scribbles and doodles on Jimmy's notepad all had her as banking law, while he was billed as a bunch of other things) and wants to pursue her passion and defend people. Even now, he's wrestling with grief over Chuck's death, and all the little ways he could "honor" Chuck are being pulled away form him. Him getting the "FUCK YOU JIMMY!" from Howard was like the Sandpiper thing. Burning a bridge to build up some other people, this time it's doing right by the firm that his brother helped establish (even though we don't know that HHM will survive the series).
With that all gone, his revelation of becoming a criminal lawyer (a CRIMINAL lawyer) is just one more step into taking up the Saul mantle.
