Why did Sabo eat the Mera Mera no Mi fruit? Does anybody know why Sabo ate the Mera Mera fruit?



I thought Luffy really wanted this fruit because it was the devil's fruit that his brother Ace ate.

Sabo took Luffy's spot in the Colosseum to get the fruit for him.
Sabo never intended to get the fruit for Luffy. When he showed up in this arc, his first words were 

"I'm not letting you have the Mera Mera fruit, Strawhat Luffy!"

Sabo always intended to eat it, and Luffy was fine with that. Luffy obviously can't eat it himself, he just wanted someone he liked to have it. He left the colosseum very happy, fully understanding that Sabo was going to eat it. It didn't come out of nowhere at all.