"Gokudera said WE decided," Riku knew that there had been a 'we' which really didn't let either squirt off the hook. "So that no one gets hurt." Which definitely implied it about about the attack on Tsuna, but didn't really give Riku any hints.
"Sora, what happened to them? We weren't even gone that long!" One minute Gokudera was being some kind of doting boyfriend, and the next they were broken up.