"I suppose I'll make you a cake anyway," Lily said.

Sirius grinned. "I'd be disappointed if you didn't."

The truth was, he knew baking for people made Lily happy. Even on his own birthday, his first instinct was to think about what everyone else wanted.

It simply never occurred to him that he might deserve to want something too.

Lily and James were, quite simply, the best people Sirius had ever known.

Loyal. Brilliant. Ridiculously kind.

Marriage hadn't changed that.

If anything, it had only made him feel more certain that he'd somehow stumbled into the greatest friendship imaginable. They had never once made him feel like a third wheel or an obligation. There had never been a moment where he'd thought, I'm intruding.

He belonged.

He loved watching them together.

The quiet conversations spoken with only a glance. The effortless way James reached for Lily's hand without thinking. The way Lily instinctively leaned into James whenever they sat beside each other. They fit together with the sort of ease that made the rest of the world feel slightly out of focus.

Sirius wasn't jealous.

Not exactly.

He simply found himself wondering, sometimes, what it might feel like to be wrapped up in something so complete.

It was the sort of thought he never intended to say aloud.

Perhaps it was the firewhisky.

Perhaps it was the warmth of the sitting room, Lily curled against his side on the sofa while James sprawled in the armchair opposite.

Or perhaps it was the way James asked, with complete sincerity, "So what do you actually want for your birthday?"

Lily's hand rested lightly between his shoulders, absentmindedly tracing lazy circles through the fabric of his shirt.

The whisky had left him pleasantly warm and far braver than usual.

Before common sense could intervene, Sirius smiled dreamily and answered,

"I'd like the two of you to take me upstairs."

Silence.

Then James laughed.

And no one said no.

Sirius woke late the following morning with a pounding headache and sunlight spilling through unfamiliar curtains.

It took him several long seconds to realize where he was.

James's arm was draped heavily across his chest.

Lily slept on his other side, her dark red hair spread across the pillow like spilled ink.

All three of them were tangled beneath the blankets.

Sirius stared at the ceiling.

Fragments drifted back to him.

Laughter.

Someone knocking over a lamp. James laughing so hard he could barely breathe. Lily kissing his forehead and calling him ridiculous.

Another round of firewhisky. 

Laughter that refused to end. Warm hands and warmer mouths. James's lips and tongue leaving him gasping out, "Merlin," while Lily's deft touch around his length drew helpless sounds from him, her delighted laughter in his ear so bright and beautiful it might have belonged to a celestial choir. 

Soft pillows.

Cool starlight spilling across bare skin. 

James's grin. 

Lily's smile

For perhaps the first time in his life, Sirius couldn't remember feeling lonely.

He had absolutely no idea what they were supposed to do now.

As it turned out...

Something rather unexpected.

A few weeks later, Lily found Sirius alone in the kitchen.

"So," she said casually, "how would you feel about moving in with us?"

Sirius looked up from his tea.

"...What?"

"You spend most of your time here anyway."

"Bit unconventional, isn't it?" he said. "Married couple having a permanent roommate?"

Lily shrugged.

"I just thought it'd be easier."

"Easier?"

"You'll want to be involved when the baby arrives."

Sirius froze.

"...The baby?"

She looked at him.

"...James didn't tell you?"

"There is a baby?"

Lily smiled, one hand unconsciously settling over her stomach.

"I think so."

"S-since when?"

"If I've counted correctly..." she said thoughtfully, "...since your birthday."

Sirius opened his mouth.

Closed it.

Opened it again.

"...Since my birthday."

"Mmm."

He stared.

Lily's smile grew impossibly fond.