Sans is a MONSTER and not a HUMAN, so he doesn't follow HUMAN biology like a HUMAN skeleton. Same with Gaster and Papyrus.   

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So peaceful... She had missed that face of his. That calm, sleeping, snoozing face from the skeleton, who she would sleep next to every night, for the last couple of years. These last few weeks where she had been without him, where her bedside had just been completely empty, it had been hell... Absolute hell. It felt cold at night when she wasn't there, it felt too silent. At least when she led next to him, she was accompanied not only by  the skeleton's arms, but his quiet, gentle snores too, which didn't end up being an annoyance to her. In fact, it only made him seem all the more adorable while he slept, as she watched over him, smiling all the while. Carefully, she went to pull one of her arms out from under the skeleton's cuddling arms, and she went to place one of her hands to his cheekbone, while just staring at him with so much love and affection. There were no words to describe just how relieved she was to know that this man was still hers, that he would still be getting married to her. 

Stirring, the monster appeared to softly groan, as he was waking up from his fairly peaceful slumber. The human continued to watch him, finding him adorable as he seemed to scrunch up his face for a moment as he yawned, until he finally and steadily blinked open his sockets, only for his calm, blank expression to be accompanied by a warm smile, once he saw Frisk staring back at him. "heh. hey." He murmured, deciding to cuddle her a little closer, now that he had woken up. He was honestly glad to see her, because part of him had been scared that last night had all just been one big dream, that felt very real, just because he was missing Frisk so horribly. However, it hadn't been a dream. She was here. She was actually here, beaming back at him, and it made him the happiest he had felt in the last few weeks. 

"Morning, honey." Frisk decided to tease in return, considering he had once said the same to her when she had woken up by his side, the day after they had gotten engaged. It felt so satisfying to see a light hue of cyan shade over the skeleton's cheekbones when she said that, and he began to chuckle, and he went to deliver a kiss to her forehead, which she didn't object to. She only giggled in return, feeling like a helpless teenager who had fallen in love for the first time all over again. 

"mornin', sweetheart." Sans poked in return, snickering with triumph when he managed to make Frisk blush in return. Really, he had missed this. Even the most simple moments of them just laying in bed together, flirting and teasing... He hated the thought of losing that. Of waking up, to Frisk's face. To seeing her smile at him, the way she did. She was so precious to him that the thought of being torn from her, (even if it was out of his own choice), felt like a fucking nightmare. Don't get him wrong, he was still somewhat mad about the choices she had made in the past; about what made him walk out in the first place. But she would gradually be able to prove herself to him, and already, she was beginning to do that. 

"You know, I'm glad we got back together, in time for Christmas..." Frisk murmured. "I still need to go Christmas shopping..." She sighed, feeling so unorganised this year. She would have done it weeks ago, had her and Sans not had so many complications in their relationship, or if she didn't suddenly become busy. Now, it wasn't even that long until Christmas day, and chances were the stores would be packed with people trying to rush to get presents last minute - including her and Sans. "Maybe we should go today..." She spoke thoughtfully. 

"christmas shoppin', huh?" Every year that type of thing was always pretty exhausting. He felt like he probably wasn't as active as he used to be, when constantly attending missions he was sent on for the Mafia. In that kind of environment, you had to keep fit, and not so lazy. He wouldn't say he was crushingly lazy now to the point it stopped him from doing anything; he definitely wasn't up and about as much as he used to be though. Running after two little kids did help keep him up on his feet though - that being Leo and Luna. 

"Yeah... I know it's stressful, especially at this time with it coming so close, but I just don't want Leo and Luna to be disappointed." Frisk mumbled, while Sans listened closely. It wasn't like they were older adults who would be fine with just a gift or two, because it was "the thought that counted", or something like that. They were two little kids who looked up to the idea of Christmas as getting at least a couple good gifts, and Frisk would be lying if she said she didn't like spoiling the two on Christmas day. Only because it was the only time of the year she ever allowed herself to spoil them. Her and Sans agreed they wouldn't want to spoil them too much, in the worry that they'd become easily ungrateful as they grow up.

You saw that happen with some kids, and it was... Just a nightmare.

"yeah, i get ya. well... give me a couple of minutes, and i'll get up." Sans told her, still keeping his arms around her as if to say she still had to snuggle with him here for a couple more minutes. Not that the Dreemurr girl really had any objections with that, as she giggled and happily stayed within her fiance's arms, feeling content. Neither of them even had to talk to fill the silence that entered the room, as even just being quiet and in each other's presence was nice enough, as they led in bed together. That of course had to be interrupted though. 

"Mommy! Daddy! Wake up!" Luna came running into the room, with her brother following behind. Upon entering the room, the two 6 year old's tried to pull themselves up onto the bed, using something they found to step on to help them up. Luna was the first to shake her parents who were already awake, until Leo joined her and decided to help. "Look outside! It's snowed!" She squealed excitedly, seeing the two parents glance at each other in surprise. Getting out of bed, Frisk decided to walk over to the curtains and she pulled them open, only to see that the twins were in fact right. Everything outside was blanketed in a fairly thick cloud of snow. It looked... Beautiful. Frisk couldn't remember the last time it had snowed in December, maybe they would end up having a white Christmas.

"Can we go outside, please?" Luna wondered. Luckily for the 6 year old, the parents had already planned to go out  today, seeing as they needed to go shopping. Maybe there would be someone dressed as father Christmas, and Sans might be able to take the two kids to see him, to distract them for a bit, while she went on a shopping spree. After all, the last thing Frisk wanted was for Leo and Luna to see her buying gifts for them for Christmas, because she wanted them to be able to keep their strong belief for Santa, only being small children and all. She missed the days where she would be so innocent. 

"Of course, go get changed into something nice and warm - the both of you." Frisk said kindly to the two children, who zoomed out of the room the moment the mother had suggested for them to do that. 

"so much for a couple of minutes." Sans joked, going to pull the covers off of himself to climb out of bed. Not that he was all that bothered. It made him glad to see the kids so happy - especially Leo. He had missed seeing that boy smile, considering for some time he had been so used to seeing the child look so glum, likely due to the fact that his parents hadn't been together for the last several weeks. But they were back together now, and Sans knew he never wanted to let go of her. That was pretty evident as he wrapped his arms around her waist from behind, while she was still busy staring out the window, and he lightly kissed her on the shoulder, and on her neck, before murmuring: "i love ya..." 

"I know... I love you too... I'm glad that we'll get to spend Christmas together this year." Because she had almost been worried it would be the first time in several years where they hadn't got to do that. And that would have upset her, and the children, so much. It would have upset Sans too. This was what was best for them, being able to celebrate Christmas...

Together.