First, i will not permit myself to think for even one second, that Kakashi killed Rin of his own accord. Neither did he do it to be able to awaken the mangekyo sharingan. So, there are two possibilities : 1) Rin wasn't herself anymore, in the meaning that someone had taken over her body etc..and was already dead. 2) Kakashi was under genjutsu or something that made him kill her.
So when Obito came to see this, he could only see Kakashi killing Rin for the Mangekyo, and Kakashi breaking his promise.
I guess that when he will see that, Obito won't be able to interact with Kakashi, because he doesn't have any Life energy yet, so he is "kind of a ghost"
In the end, Obito who could interact with Kakashi, got mad and went to the dark side of the force and got evil, all of that because of a misunderstanding.
You have a point there, but bear in mind that
Obito is well aware of what happened to Rin. When
Kakashi asked him something, I remember him saying
"You let Rin die." He didn't say
that Kakashi killed Rin, so its not really all a
misunderstanding. Its just Obito's choice to
turn evil. Which is not really surprising because
Uchihas, as I see it, has a great tendency to turn
evil. Besides, the most sinister of all, Madara,
is there to influence him everyday. I dont
suppose you would expect him to remain good, do
Don t you have to kill your best friend to get
mangekyou sharingan. Obito didn't kill
anybody so I think as long as either him or
Kakashi acquired MS the other eye would also
transform. Also their is definetely a good reason
for Kakashi killing Rin