Kuroko was the first to say it. The three words that sealed his fate, even when he didn't know it yet. He had said it to Aomine when they were still at Teiko, an accident really, but that didn't make it any less true. Although Kuroko may have been a bit more naive when he decided to say it to the dark haired teen, he was sincere. What he didn't know was how those three words had shattered Aomine's world at the time, and his distant attitude and selfish remarks were the only thing to keep his heart at bay. He would never forgive himself for hurting the one person he cared for the most. But he couldn't bring himself to repeat the words back to those hopeful, beautiful blue eyes. Nothing good could come of something like this and Aomine knew if he gave in now it would only be worse when it couldn't work later.
Needless to say Kuroko was devastated but he made his decisions accordingly, pushing aside his grief and moving moving moving until he found himself at Seirin, playing basketball alongside someone who didn't have to pick up the pieces of his broken self, but rather held him together and slowly filled in the cracks. After learning about Kagami and Aomine's unexpected meeting, Kuroko was apprehensive, but couldn't deny the sight of the newly lit fire in those red eyes he had learned to love.
When the three of them had begun to come to terms with the past and the present, they started looking to the future and slowly old wounds mended and the scar tissue made them stronger. The adoration Kuroko felt for these two boys was greater than any grudge he could ever hold. Seeing the way they looked at each other made his heart swell and his head feel light, and the feeling was even more powerful when they directed those special looks at him.
When he first said them to Kagami, the taller boy was shocked to be brief. Kuroko was intimidated by the possible outcomes that would come along with saying these words, but he said them nonetheless. But the reason it was different this time was because when he decided to admit his feelings toward Kagami, he was sure of himself. Not like how he had been those few years ago. They had been walking home and just as they were about to part ways he turned to Kagami and, with all the bluntness in the world, let him have it. He remembered how Kagami blushed and fidgeted but stated with all his sincerity that he felt the same.
When they kissed at that rusty stop sign it was completely different than the first kiss they had hastily shared on the court in front of anyone who wished to look their way. This one was slower and happier and more well thought out. Kuroko even managed to wrap his arms around Kagami's neck and hold on so he could reach more properly and save Kagami the strain of bending down too much.
On the day that Aomine shouted those words into the rain Kuroko felt the relief in all those heavy droplets cleanse him of all his worry.