You were an extrovert, and he was an introvert. And as it typically goes, the extrovert "adopts" the introvert. He was a "sad little thing", according to you. (He most definitely was not.) You'd seen him sitting alone in a corner one day, and decided from then on that you'd always be by his side. Wherever he was, you were never too far away.
He was sitting on the couch, enjoying a book. And who should walk in with a lopsided grin? None other than you of course. You greet him with a smile, and in return his face is the same deadpan expression as always.
But nonetheless, when you leaned your head upon his shoulder he made no effort to push you away. And you smiled because that was more than enough for you. You knew that deep down, he valued the connection you guys shared. Even if he may not be as expressive as you were.