OBITO BRO THERES OTHER FISH IN THE SEA...
SHE NEVER EVEN WANTED YOU FAM, YOU GOT FRIENDZONED WHILE SHE WANTED KAKASHI
1. You have no idea how powerful love is. The argument "there are other fish in the sea" shows how bad your comprehension of the term "true love" is. If you think
"okay, she's gone, next one pls." then you didn't feel true love in your life, sorry. Obito loved her so much, that he would've done everything to keep her safe and happy. That is a really distinguished attitude.
2. It doesn't matter if love is returned or not, Obito cared so much for Rin. More than he could care for anyone/anything else. He wanted her to be safe, healthy and happy. Just look at his final words, before he thought he would die and ended up in Madaras cave.
Also, he didn't start a war because of Rin. Are you still too ignorant to realize that?
He started a war because the world, which made so many people suffer, was cruel, so he wanted to change that.. in order to avoid that someone else would have to to experience a loss like he did.