There were those who said Arthur wasn't affectionate, but that wasn't true.
Alfred knew that Arthur was simply different than he was, he had his own ways of showing his feelings, and while he wasn't as obvious and physical about it as the younger was, Alfred had grown accustomed to the small things he did, learned to interpret them. Sometimes it was simple things, such as Arthur reaching over to touch the underside of Alfred's wrist when he wanted his attention for something; or when he would squeeze Alfred's shoulder when he could see that he was upset and no one else could, a gentle squeeze that always lingered a bit longer, comforting in a way that most would things was simply polite. There was also things such as the way Arthur would casually move his foot forward and brush it along Alfred's leg in a way that was seemingly accidental, when they were in public and he knew Alfred wanted to hang on him and kiss him like he normally did. Those little touches, to Alfred, meant more than a million words ever could, because they conveyed those thoughts and feelings that Arthur was never quite sure how to convey, that usually ended up just making him flustered and stumbling over phrases to try and describe his emotions. Arthur could say so much more with a simple touch on the wrist, or a gentle caress to his cheek, than a simple "I love you" or some such phrase.
Arthur knew Alfred's odd quirks too, of course, although people never really held him to such subtleties, but the brash nation had his moments too, small things that Arthur learned to cherish. Sometimes, they would be standing and Alfred would simply drop his head down onto his shoulder from behind, and Arthur knew in those times that it was best not to say anything, not ask what was wrong even if he could feel the larger frame behind him trembling for some unknown cause, because he knew that Alfred had his pride and that sometimes he just wanted someone to be there. Those times he would simply reach back and take Alfred's hand in his own, or turn and kiss his cheek, lead him over to the couch for some impromptu cuddles or a movie, and they wouldn't ever speak of it again. Sometimes at meetings Alfred would sneak his hand under the table and curl his fingers around Arthur and squeeze a couple times, just briefly, and then he would pull his hand back, and Arthur would smile at the light pink that dusted his cheeks afterward usually that no one else would really notice, but Arthur would.
And sometimes, too, there were days that they could be alone, where they could snuggle up to each other, curled in a way that fit perfectly, for hours until the sun was already high in the sky. Alfred would shower Arthur with little kisses, long fingers tracing intricate, nonsensical patterns onto his skin, and Arthur would laugh lightly, lips curved into a warm smile that was Alfred's alone. Arthur would kiss him too, soft pecks on the lips, little brushes against his neck, accompanied with blushes and embarrassed huffs that made Alfred chuckle and kiss him full on the lips, strong arms wrapped around him as if he could hold him there forever, as if they wouldn't be parted once again, inevitable. There would be long days of lying across each other on the couch, legs and arms tangled in a way that made sense only to the two of them, lips lingering in a smile against each other's. And there was the sensual touches, fingers ghosting over each other's bodies and skin pressed up flush, moving together, breathing together…and then it would start all over again in the morning. There was the goodbye that always came, lingering kisses and fingers trailing across each other's as one or the other walked away toward airport gates to a plane that would take them once more over that cursed ocean that divided them, but they would take comfort in knowing that they would have those little affections once again, someday. It was those small things that only served to make their bond stronger in ways that no one else could really understand, because these small affections meant more to them than anything else in the world. They were things that were theirs and theirs alone, communicated things that words could never say, and it helped create a love that nothing in the world could ever destroy.