Uhhhh, try again.
He wasn’t shocked when he was looking at the corpses in the temple because he already felt their deaths. But in the temple scene he was clearly sad and hurt. Just the way he says “Padawan” makes it so obvious.
This image is technically from a later scene but he makes the same kind of expressions, and this also shows that he was clearly distraught that Anakin fell to the dark side and murdered Jedi.
He went to fight Palpatine because they needed to destroy the Sith to try and bring back the Republic as soon as possible. I’m surprised your faulting the guy who’s famous for saying “Do, or do not, there is no try” for actually attempting to DO something about the horrible things that have transpired. You’re seriously suggesting the two remaining Jedi should’ve just never tried to stop the Emperor? “Screw this, go get drinks, we should, Obi-Wan. Forget the Sith wreaking havoc on the galaxy, we should. Only allowed to sit on cushions, we are.” Like, how DARE the heroes try to stop the villains!
It was only after realizing that the Emperor already won and that he can’t beat him that he flees, that it would be better for him to exile himself so there’s hope for a future for the Jedi.
Don’t forget, in the original trilogy he wanted Luke to kill Vader and the Emperor. The Jedi are not above killing Sith when they need to.