When Light said those three little words, those three magical words, L became putty in Light's capable hands. After all, how could he not? He had said those words… those amazing, beautiful words that L had always wanted to hear. Honestly, no one had ever directed those words at him before, except for maybe Watari, but he didn't count. This was different.
This was Light.
It was then that L was sure that Light was in love with him, and equally sure he returned the coveted feelings. He simply couldn't resist, not after Light had said those three words. L felt Kira could kill him now – or maybe a few minutes later, so he'd have time to take Light up on his offer – that he could die, die happy.
And so it was after very little thought that the detective glomped the unsuspecting teenager, kissing him fully on the lips. "I love you, too, Light-kun," he said, smiling adorably – because we all know how adorable L is when he smiles.
"But I –" Light tried to talk, but was cut off as suffocated him in another kiss.
'He tastes like cake,' L thought dreamily, 'just as I expected he would.'
L was so blissfully happy, that even when Soichiro walked in on the detective straddling his very confused and slightly scared son and blew up in Ryuzaki's face, it couldn't put a damper on his mood. After those three words had been said, by Light of all people, nothing could.
And what were those words that made L so uncharacteristically happy? It's simple, see, a minute ago, Light had turned to Ryuzaki and said:
"Want my cake?"