Although L no longer thought of Matsuda as a complete idiot, that didn't mean that L suddenly thought that Matsuda was a genius. He was now more observant of the younger detective, always looking over with interest whenever Matsuda offered his opinion on the case. His interest in Matsuda had grown ever since the night when Matsuda drank a cup of sugar-filled coffee; not many people would touch the stuff, so the fact that he had found someone like himself made him very curious indeed. And while Matsuda did notice the sudden increase in attention, he assumed it was because he was doing a better job instead of thinking that L was just curious about how Matsuda worked.
Whenever something would come up that required all the members to sit together, L would always make sure he was next to Matsuda. The first couple of times, no one really noticed it, but then it slowly dawned on everyone that Matsuda and L were sitting together all the time, which naturally sparked some questions about L and Matsuda's sexuality. Matsuda didn't think anything of it, but he was Matsuda, if that explained anything. And L? L simply wanted to sit next to Matsuda, as if just sitting by the brunet would help L figure everything out about the younger man.
In the time in-between meetings, L would often sit next to Matsuda.
"Matsuda's not exactly smart," was the only explanation he would give, and although there was still suspicion the others would wave it off. Matsuda remained clueless, as usual. And he continued to drink coffee with loads of sugar in it too, at night. During the day he had water, because "he was short enough already and didn't need to stunt his growth by drinking excessive amounts of coffee" or so he claimed.
Coffee so did not stunt growth. Too much, anyway.