But if Obito thinks that Kakashi killed rin! Then it would have been silly for him to say his reason was because Kakashi let rin die! He would be like you F***ing killed RIN! When asked by Kakashi of why he did everything he has done up until this point in the series.

I don't know this whole thing does not make sense unless Obito realizes that Kakashi did not do it on purpose then it might make sense.