The truth is why Obito made this war.
So Rin death is not the main reason.
I smelled something strange when Kakashi killed Rin:
Obito feel pain , some branches and some black sticks are growing to a moderate size ( one meter approx ).
He does a great job to go protect Rin's corpse and Kakashi from the masked ennemies:
he uses great death shots combos that he just learned in the cave and his intangibility from "kamui" .
He is master of his mind , Rin is dead.
Until he brakes a mask...
Obito sees the face of one of the masked guys ( if you look carefully this guy wear a konoha headband ), the masked guys becomes perplex ( why just now that the mask is broken? there is something ) , Obito tightened his fist and...
He feels pain like if he was in hell and huge branches have grown ( +/-30 meters ).
Rin death=1m branches+ little black sticks.
See the face=30m branches.Do you see what I mean?
Naruto is the only one that knows that part of the story.
Naruto's reaction : crying and then smiling "I'm gonna tell that to everybody".
I think the truth is the identity of those masked guys.
What if the guy was Obito's father or brother ...
Your love and your best friend commit suicide to keep a big weapon away from unknown ennemies.OUCH 1 meter high.
The ennemy was in fact...... your village! ( or your clan ) that your love and best friend were trying to protect.OUCH 30 meter high.My whole world is broken.
Can't wait , what's your opinion?
Have you got an idea of what is that truth?