Up until his relationship with Harry, Severus had led a rather dissolute life. Few people were interested in more than a quick shag or three with him, and none of them wanted a long-term relationship. Most people only had sex with him as an attempt to get what they wanted (Severus usually saw through this ploy).
Severus was of the mind that even impersonal sex was better than none. Consequently, he had behind him hundreds of one-night stands, relationships of convenience, and absolutely no experience with love or affection.
Harry's sexual history was radically different from Severus'. Harry had had few relationships, all of them serious.
It was no surprise that Harry was the more obviously affectionate of the two. He was more likely to touch Severus non-sexually, more likely to say 'I love you' not mid-coitus, more likely to smile affectionately at him even in public.
Severus cursed himself for not being able to reciprocate. For that clog in his throat every time he tried to say, "I love you, too." For that bloody paranoia which stopped him from smiling back at Harry. For his inability to touch Harry sexually.
He knew that Harry loved him the way he was, that Harry would tolerate his… coldness, but Severus didn't want Harry to tolerate it. He wanted to be as open, as loving, as Harry was.
He looked at Harry, who was cheerfully preparing dinner. Harry was whistling some appalling Muggle tune, but Severus smiled slightly nonetheless. Harry's exuberance was infectious.
Severus opened his mouth. Closed it again. Opened it and moved his lips. Nothing came out. He cleared his throat slightly and tried again. Nothing.
He fought back tears. Damnit. Seven long months and he had not once been able to say 'I love you.'
He knew Harry wanted those three little words. He knew Harry wasn't trying to make a fool of him, wasn't about to blackmail him, wasn't going to hurt him purposefully…
He could not make the words leave his mouth. He couldn't even form them.
He stared at himself in the bathroom mirror that night and practiced. Damnit, he should at least be able to say the words. If not to Harry, at least to thin air.
Apparently, even thin air was undeserving of his declarations. Of course. They were meant for Harry.
Harry entered and wrapped his arms around Severus' waist. "I love you," Harry murmured into Severus' shoulder blades. "God, I love you so much."
Severus opened his mouth to say the words back.
"Harry…" he began, trying to form the next words. "I… I…"
Harry kissed his back.
"Don't," Severus said simply. "I need to… to say this. I… I have to. At least I have to try."
Harry turned him around and looked at him worriedly. "Are you okay, Sev?"
"No," Severus answered. "I need to… Harry."
"What?"
Severus stroked Harry's cheek softly. "Harry… I love you."
Harry smiled widely. Apparently Severus could overcome the habits of his formerly dissolute life.
Dissolute – adj. Loose in morals and conduct; marked by indulgence in sensual pleasures or vices. Word of the Day, February 22, 2008)