It's actually very simple to forget people. Even those you really care about.
It's a rainy day when Luke Smith bumps into a tall, dark-skinned man on his way into a coffee shop. The man had been on his way out. Naturally, Luke mutters an apology and excuses himself, so when the man doesn't reply, Luke can't help but think he's rude. Very. Rude.
(Clyde is seventeen when he first kisses a boy. It was his first big experiment, really, and he finds he likes it much more than kissing girls. It was much more exhilarating than chasing after aliens no matter what Luke says about kissing. And Clyde will never forget that moment when Luke Smith would just not shut up and Clyde could not think of anything but Luke Smith, and kissed him to shut him up and Luke realized that kissing was a lot more fun than chasing aliens.)
Luke finds the oddest things in his flat sometimes. He's twenty-six and living on his own in a nice, if not, messy flat in Cardiff. Once, he'd decided to do some cleaning and he was rifling and rummaging through piles of notes on various aliens he had countered and digging up old photographs of months just after his activation when he happened to dig up a pack of inking pens.
He frowns at the pack: he doesn't draw and he doesn't know anyone who can draw well enough to use it. It was strange: they looked well-used and worn, but he would swear up and down the street he lives on that he has never seen it before in his life. Still, he stares and sees the empty slot for the missing pen.
(Clyde's fingers slip in through Luke's thin, boney, long ones (always pale). They're long and thin and boney, but Clyde liked them. He liked feeling how Luke's cold skin would become warm because of his. ("Actually, Clyde," Luke had explained, "it's you who is cold… and you only feel warm because my heat is being transferred to you. Law of thermodynamics, Clyde." Clyde had smiled and answered, "Whatever.") It's the first time they hold hands and Clyde finds comfort in Luke's hands. Luke turns to him, smiles, and mouths I love you and Clyde's heart melts. He answers I love you, too.)
On the days that he finds time away from Torchwood, he takes a train from Cardiff to Ealing and manages to always surprise his aging mother with a lovely bouquet and some alien artifacts. It's on those days that he then finds himself spending the day having tea with his mother and running across the street to greet the Chandras. When he can stay the night, he goes up to see Mr. Smith, to say hello to K9, and to spend the night remembering secondary.
Sometimes, he just sits and surveys the attic. It is those times that he feels something is missing and his mind is always reaching out, trying to remember what he's forgotten.
(But Luke Smith never forgets, remember?)
(Clyde and Luke are eighteen and are at university. Well, Luke would say "university" and Clyde would roll his eyes and correct him: "It's uni, Lukey, no one says university!" They're living on campus and alone and studying in different places, miles away. But Clyde finds time to phone Luke every night and the two of them would talk until they're too tired to do anything, but listen to each other breathe.)
Sometimes, Rani or Maria holds a get-together-party for their secondary friends. Luke almost always goes—Torchwood wouldn't allow it otherwise—and in the middle of a story, in a middle of a re-telling, or even in a joke, he catches Rani or even Maria staring at him and then at the empty space next to him, as if someone else is supposed to be there.
His hands feel strangely empty whenever this happens.
(They move in together, into one flat, when they're both out of university. Luke decides to intern at Torchwood (wherein Sarah Jane had fainted when she heard the news) while studying forensics in grad school. Clyde chooses to pursue art and writes fictional comics based on their adventures on Bannerman road.
Clyde's very messy: he leaves his things all over the place.)
He accidentally spills coffee on Luke a couple days later when he bumps into Luke again. This time, Luke is too much in shock at having bitter black coffee spilled down his front to say anything. But the tall, dark man flusters and apologizes right away, handing him a few napkins and beginning to mop him up. Luke stammers thanks and the man offers to buy him a drink, which Luke accepts.
(They get into a fight right after Luke finished grad school. Luke wants to move: get away from Cardiff, from London, from England. He wants to move out of the country and he finds a job out of the country where he could get away. Clyde doesn't want to leave, doesn't want to move into a bigger house, doesn't want to leave England, leave home. He hates change.
Things changed anyway.)
"I'm Luke Smith," he says, offering a hand once they're situated across from each other in the booth. Something flickers in the man's eye, but it's gone almost as soon as it appeared, so fast, Luke thought he'd imagined it. Without knowing why, Luke added: "how do you do?" (and mentally winced, though he wasn't sure why).
The man smiles and takes Luke's hand, somehow feeling right. His hand doesn't feel cold.
"I'm Clyde," he says, "Clyde Langer."
When Luke and Clyde (and Maria and Rani and Kelsey Hooper, and that kid a few doors down the road) are twenty-one, there's a man who creates forgetfulness. People begin to flock towards him and his office, wanting to take this new operation for a spin. He makes a lot of money because of this. People want to forget.
(Clyde prods Luke's arm.
"Have you been working out?"
Luke glances down at his arm and blinks several times before answering.
"Well, I've researched about college life and they say that there's a high chance of catching the Freshmen-15, where the first year students somehow gain 15 extra pounds after their first year of college. I thought, to prevent this from happening, I should eat a balanced diet, complete with the necessary nutrients, right?" Here, Clyde nods absently, still poking Luke's arm. "While on that thought process, I thought I should begin to exercise as well, to develop my muscles and transform the fat into muscle, to become more fit." He pauses for breath and waits for Clyde to say something. When he didn't, Luke casts a glance at Clyde.
"Clyd—mmmrph?")
The thing is: it is actually very simple to forget people. Even those you care deeply about. They just have a way to get back to you, even when they've forgotten as well.