I'm probably super late and you guys might of already talked about this but. After reading Hell 605 I've come to the realization that the reason why Kakashi asked Obito why he isn't gonna blame him for Rin's death is because in chapter 605 page 7 he shouted out "I'll Never Acknowledge it!!" meaning he doesn't want to believe Kakashi killed Rin. Thats why he didn't blame Kakashi for the death of Rin.
As for why he killed Rin I wasn't really clear on. Everyone kept saying that its because she was a spy but for some reason that doesn't sit well with me. I think Her body has something they want obviously and Rin finds out that they need her Tells Kakashi to kill her so the enemy wont get what they want from her. And the reason behind her facial expression is because she didn't see the hit coming and that'll explain kakashi's crying.
What do you guys think?