The first time that Sirius says I love you to Remus is, possibly (probably, undoubtedly), the most embarrassing moment of his entire life.
He's tracing meaningless patterns on Remus's chest, gazing dreamily at him as they lay together. Remus, telling Sirius vehemently that he was going to finish his book and no amount of puppy eyes would sway this decision, had denied Sirius sex, but had said that he could lie in bed with him as he read, though if he consciously made an effort at being distracting he would kick him out. Sirius thinks—in his own thoughts and his own thoughts alone—that this isn't bad; it's the opposite, rather. Watching Moony is, very, very secretly, one of Sirius's favorite pastimes.
Remus is lovely, for lack of a better, less vomit inducing term. Sirius thinks that Remus would know a better word for it, being rather like a walking dictionary and all, but the day that Sirius asks him this is the day that James stops looking at Lily as if she were some divine goddess.
Remus is lovely because he always seems to manage to catch Sirius's eye. Sirius watches the way that his chest moves up and down as he breathes and the way that the corners of his mouth curve up ever so slightly and his eyes twinkle when he comes across a part in a book that causes him a positive emotion of any sort. Sirius notices all of his scars and freckles and finds beauty in each one. Sirius sees the small things that Remus subconsciously does in different situations; the small, gentle smile that no one except for Sirius notices when he or Prongs or Wormtail or a combination of the three do something charmingly stupid, for instance.
Sirius perceives little things about Remus that he would bet that Remus doesn't even know. Sirius thinks that knowing so many small, irrelevant things about someone should drive him mad, but every time he discovers something new he just experiences another rush of…something. Something that is pleasant but at the same time unspeakably horrifying.
Sighing in content, Sirius rests his head against the pillow and lets his eyes scan over Remus's body. Closing his eyes, Sirius says, "I love you," and then immediately wrenches them open again.
Everything stops. Time, space, Sirius's heart, the steady ticking of the clock on the nightstand beside Remus's bed. Remus is looking at him in shock, and Sirius's face drains of all color. Sirius does the only thing he can think to do. He bolts.
Or, well, he would have bolted. Instead, he manages to get himself caught in the curtains surrounding himself and Remus. Sirius is quite sure that he is going to die. Though, whether from embarrassment or suffocation he's not sure.
Unfortunately, the act of entangling yourself in curtains, ripping them away from the metal holding them up, and landing in a loud, ungraceful heap on the floor is one very likely to wake up anyone sleeping in the near vicinity. Said people would happen to be James Potter and Peter Pettigrew.
"What is going on?" Sirius hears James say sleepily as he lies in his curtain-mass of shame. No one answers him.
"Is that Padfoot?"
Suddenly, the curtains are maneuvered off of him, and Sirius is met by the wand-illuminated faces of James and Peter. "I'll say it again," James says, "what is going on?"
"I…curtains." It's nowhere close to a sentence, but it's the best that Sirius can do in his current state.
James looks from Sirius to Remus. "Moony, what is going on?"
"Well, obviously, Padfoot isn't fit to tell you anything at the present time, so I suggest that we all go back to bed and discuss this, if we are quite ready, in the morning."
Sirius can see James giving Moony a skeptical look. Sirius hopes that he won't push the subject. James sighs. "You're both bloody secretive prats, and if my brain wasn't sleep-fuddled I would question you more."
"If I wake up again tonight I'm hexing someone's bollocks off," Peter grumbles, collapsing onto his bed. Typical of Peter not to give a rat's ass about anything until he's eaten half of the entire kitchen at breakfast.
"Right there with you, mate," James says, getting into his respective bed. "Sirius, no more curtain escapades until we're all wide awake!"
No one speaks for a good ten minutes or so. Sirius hopes that he will sink into the floor. He recognizes the fact that sinking into the floor would probably cause him to fall to his death, but he doesn't think that he would mind this fate all too much.
He starts to get up and perhaps run to go sleep on the couch in the Common Room, but, softly, Remus calls out to him, "Come back to bed, you stupid git." Remus mutters a quick, "Reparo," at the mangled curtains. They rid themselves of any tears and float back up to their original spot, where they had peacefully hung until Sirius had assaulted them.
"You mean that I didn't—"
"I told you to come back to bed, so come here."
Hesitantly, Sirius edges back to the bed and slips under the covers. "I didn't…ruin anything, did I, Moony?" Sirius looks at him in anxiety,
"Ruin anything? You really are thick, aren't you, Sirius?" Remus initiates an amazing kiss and says, eyes glowing and smiling in a way that he only does when he's really happy, "I love you too." Sirius's grin is so wide that it makes his mouth hurt.
"Can I persuade you to finish that book later then?"
With a gentle laugh, Remus says, "You're lucky I love you," and casts a silencing charm around them.
Sirius may have severely embarrassed himself, but he doesn't regret telling Remus that he loves him for a single moment.