Of course it would be Bart's idea.
He wasn't nearly as naïve as most people thought, but he was oddly innocent. Tim liked Kon. Kon liked Tim. So Tim and Kon should be together. Neither of them knew this, of course, but then they could be oblivious.
Only… Kon did like Tim, but he also liked Bart, and was more comfortable with him. He was always afraid of falling short of Tim's expectations. Bart had no expectations. Neither did Tim, but there was a weight to his regard, not the freedom that could be found with Bart.
Tim also liked Bart. The ease of just being with someone who might not always understand, but accepted you anyway. Kon accepted him, too, but didn't think it would matter if he didn't understand.
And Bart, well, Bart liked a lot of people, but Tim and Kon were his best friends. How could he not be comfortable with them, and accept them for all they were…and were not?
So of course things got more complicated.
Tim would never say anything for fear of changing what they had into something worse because he'd fucked it up. Kon would never say anything for fear of changing what they had into something better, only for him to fuck it up.
Bart was the only one saying anything, but that was all right since Tim and Kon were shocked speechless by what was coming out of his mouth. He thought it was possible this would fuck things up, too, but things didn't have to stay fucked up forever. After all, Tim eventually stopped brooding all the time, and Kon eventually stopped moping all the time after their recent respective crises, and romance wasn't even nearly as depressing as death and destruction, right?
Bart tended to see things through rose-colored goggles. But he also recognized that the main problem with relationships going 'KABOOM!' was a lack of communication. And while Robin, as a Bat, was uncommunicative at the best of times, and Kon almost never talked about anything serious, if there was one thing that Bart was good at, it was talking.
So talk he did. Slowly – even by the reckoning of objective time – clearly, with short, concise statements.
Tim liked Kon. Kon liked Tim. Bart liked Tim and Kon, and they liked him as well. So of course they should all be together.
Tim didn't think it would work, but wanted it to. Kon was afraid it wouldn't work, but was willing to try if they were. And Bart…well, Bart was smarter than anyone but Tim and Kon gave him credit for, and he'd put a lot of thought into this. Into them.
Of course he had. Tim and Kon were important him.
And this…this was one of Bart's better ideas.