If kakashi killed Rin cold hearted, Obito would of taken revenge right away or sometime after mastering his ms. Or even at the time when he faced kakashi and konoha group during the Itachi vs Sasuke fight or when Tobi came to speak to Naruto during the kage summit. It is weird how he didn't kill Kakashi or even say a thing to kakashi about Rin when they met after so long, its like he didn't even notice kakashi throughout the series. He only sees kakashi as a failure who failed to protect Rin.
I wonder why he's acting so random?