A/N: I'll confess, I love sad Star. And I also love Starco. So here you go. Let me know if I should make this a chapter story.

Christmas time.

The holiday season had snuck up on Star Butterfly. Normally, she would have been super-duper excited to celebrate her first Christmas with the Diaz family (her first Christmas ever, actually, since Mewni had its own holidays) but she couldn't find the energy to be as cheerful as she normally would have been.

Maybe it had something to do with losing Glossaryck. Or maybe it was her mother's disappointment at hearing about the lost spellbook.

But as Star trudged downstairs the morning before Christmas to the smell of Mr. and Mrs. Diaz cooking breakfast with laser puppies at their heels, she felt it could also be the strange feeling that threatened to shrivel her stomach into poisoned sludge.

"Where's Marco?" she chirped with forced joy, already knowing the answer.

"Merry Christmas, Star!" Mr. Diaz replied, flipping a pancake with a spatula. "Marco left a while ago to give Jackie a present!"

"That girl is so perfect for our boy," Mrs. Diaz cooed. The two of them giggled. They weren't paying enough attention to notice Star's hurt expression.

"That's… that's great!" the blonde princess finally managed. The adults nodded, too happy to notice her discomfort. "Well, I'll be in my room… till he comes back…"

Mrs. Diaz turned from her husband. "Star, don't you want breakfast – ?"

But the girl was already gone.

Star buried herself under the covers of her bed, trying to sort out her feelings. Yes, there was the pain of losing Glossaryck, but that hardly compared to the loneliness she was feeling.

But she'd felt lonely before. Rarely, but still. This was more than that.

She couldn't explain this feeling, nor did she know what to do about it. It was sharp and deep in her chest, and it wouldn't go away. She couldn't explain the anguish she felt at hearing Marco say Jackie Lynn Thomas's name with adoration, or the urge to scream that came upon her when Marco was anywhere near his girlfriend. It was an entirely new emotion to her, and she didn't have a clue what to do about it.

Logically, she knew she couldn't be mad at either of them. Jackie was really sweet, and Marco was absolutely adorable –

She cut off her own thought reflexively, then wondered why. She'd thought those things before, hadn't she? Marco Diaz was her best friend! Of course she thought he was adorable, and of course she loved him!

Oh.

Instantly, her stomach curdled even more. No. She wanted him to be happy. And he was happy with Jackie. Why couldn't she be happy about that?

You know why, a traitorous voice in her head whispered.

Star buried farther into her covers. Maybe she did know. Maybe it was suddenly making a lot more sense as to why she was feeling this way. But that didn't make it any easier.

At that moment, the door downstairs shut, and footsteps padded slowly up the stairs.

"Star! Star, it's Christmas Eve! Why didn't you have breakfast yet?"

Marco was back. He poked his head in from behind the door with a kind smile.

He wasn't really surprised that Star hadn't gone down for breakfast. She'd had less of an appetite since losing Glossaryck. But he'd at least expected her to regain some of her pep for Christmas.

Star didn't move from underneath her mountain of covers. She couldn't talk to him, especially not now that she knew what was bothering her.

"Star?" Marco tried again, walking over to her and sitting on the edge of the bed. "Are you okay?"

Star almost laughed into hysterics. What gave him that impression? But she only curled farther into her covers.

"Are you worried about Glossaryck?" Marco asked softly. It wasn't often, but he would occasionally catch her in moods such as this. Each time, she used the same excuse. This time, she decided, would be no different.

"Y-yeah," she mumbled. "He would have liked Christmas…"

Marco leaned over her, embracing her in her fluffy cocoon. Star tensed, immediately thinking of Jackie. Hugging, which had once felt so natural, was now a reminder not to get in the way of their relationship.

"Um, let's go downstairs," she said quickly. "I think I'm ready to eat some yummy pancakes now! Okay? Come on!"

She extracted herself from her blankets and bolted out of the room, leaving Marco feeling very concerned. There was a certain tone in his friend's voice whenever she was faking her normal attitude, and he detected it now. The problem was, he didn't know why. Maybe she just didn't want to trouble him. He was her friend, and he was always there for her, but if she didn't want to talk, he wouldn't make her.

"Wait up!" he called, racing after her, only to find that she had stopped short, staring at the kitchen down the stairs.

"Hey, Star," said Jackie Lynn Thomas, raising a hand from where she was eating her pancakes.

Star stood, frozen. Marco smiled at Jackie, not noticing, but Jackie tilted her head at her in amused confusion.

Star snapped herself out of it and said, trying to look casual, "Hi, Jackie. I didn't know you were here!"

"Yeah. Marco invited me. I'm not gonna be around tomorrow with celebrating and all, so I'm hanging around here today." She smiled.

Marco hopped down the steps to his girlfriend's side, taking her hand and leaving Star with an overwhelming sense of loss. "Do you like the pancakes?" he asked eagerly, albeit nervously.

"Like them? I love them." Jackie turned to his parents. "Thanks, Mr. and Mrs. Diaz."

None of them saw the heartbreakingly anguished expression on Star's face.

"You are very welcome, Jackie!" Mr. Diaz said proudly. "They are made with our secret ingredient!"

Jackie chuckled, and Marco turned to Star, who was still standing on the staircase. "Star, you should try them! I promise, they're almost as good as my nachos!" he said, trying to cheer her up from earlier.

Star blinked back the wetness in her eyes and pasted on a smile.

"Thanks! But I'm not so hungry. Maybe later!"

Marco frowned at her forced behavior, but it was soon forgotten as he and Jackie ate their pancakes with his parents making ridiculous conversation that made them almost choke on their food.

A single teardrop slid down the heart on Star's cheek.