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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Lonely. Just that word alone to how Frisk felt was a complete understatement, while she was lying beneath her bed covers, staring towards the ceiling, feeling pretty restless. Glancing towards the side of the bed that would normally be occupied by Sans, of course it was still empty. Their break up hadn't just been a nightmare, but reality; somehow she didn't feel like she was capable of fixing it. She didn't have the nerve, while she continued reimagining that expression of disbelief that was plastered across his face. He had looked so hurt. Hurt, by her. Normally, she was good at making him feel positive, of stopping him from falling into a rabbit hole of thinking one cynical thought after another. Now, she was likely only the cause of his negative thoughts. She was the cause of her own.

Despite feeling quite uneasy, her eyes did keep trying to flutter closed every so often; she tried to fight it, knowing that if she fell asleep, she probably wouldn't have a pleasant, dream filled rest. Instead, it would likely be filled with nightmares about how much of a failure she had become as not only Sans' girlfriend, but as a mother. Not only had Sans been fierce with her; their son had been disappointed that she never showed up. He had been so mad, that he had decided to go with Sans, likely not wanting to be anywhere near her. To him, she had been a let down. She knew that, fully well. 

Tears had streamed down the little boy's face, while he had hugged his father's leg with desperation, clearly not wanting to look at her. Why would he want to look at her after what she did? To an adult, something like someone turning up for something, may not have been that big of a deal. However, to a child, especially if it was their parent, it meant everything. It meant the world. Yet, she hadn't been able to give him that, despite her promise. She had wanted to be there. She really had. When knowing she had been late for the play, not only did she feel horrified with what would possibly happen to her and Sans' relationship, but she felt an immense sadness, knowing she had wanted to see Leo and Luna, in their little outfits, performing on stage. 

Maybe she really shouldn't have said anything. Maybe she shouldn't have decided to take on the responsibility of being the Mafia boss. Just thinking that, even while she was sleeping, made her want to curl up into a tight ball, while she sobbed her heart out within her sleep. She wanted to be positive, she wanted to see the light at the end of the tunnel, like she always did. She wanted to see that there was some good outcome to all of this, that she hadn't actually torn apart her own family. But for once, she couldn't see that light. She couldn't see anything. All she could feel was hurt, and it was her own fault. It wasn't Sans' fault. It was hers. Only hers. 

While she continued to cry, her eyes were clenched shut, as her body clearly felt like it couldn't relax from all the stress that was upon her mind right now. She just wanted to cry, and cry, and... Wait, what was that? For a second, her breath caught in her throat, as she could have sworn she felt something brush across her hand. Was that in her dream, or the real world? No, it didn't just feel like a brush, but like someone was resting their hand on top of hers. Slowly, she wanted to blink her eyes open, she wanted to see who the source of the sudden warmth on her hand was. Was it...?

"S-Sans...?" Frisk blinked in confusion, like she was genuinely amazed that he was there, staring back at her. No. There was just no way. It was just her imagination, playing tricks on her. Her brain knew what she so badly wanted, so it only wanted to tease her, to laugh at her, and hold what she wanted just barely out of her reach. Sans wasn't here. He couldn't be. There was no way he would be. Not after she let him down. Not after she let Leo down. "...I know you're not here... There's no point in playing pretend." 

"what do ya mean? i'm right here, see?" Sans warmly smiled, going to take her hand that didn't have his hand already placed upon hers, only to place that freehand on his own cheekbone, as if to prove that he was physically there. However, it felt too good to be true. Sans wouldn't just come back, acting as if nothing ever happened. She knew him. Because she had upset him, over and over and over again, it would take more than a couple of apologies and probably a few hugs and kisses just to make everything feel better. He wasn't here. 

"No you're not. This is just a stupid dream... Just please, leave me alone... I'm a bad mom, a bad girlfriend... I..." Frisk found herself sobbing once more, feeling like she was aching from the inside out. She so badly wanted Sans. She needed him. Life just wouldn't feel the same if they weren't together anymore. But she didn't know what to say, how to approach the current situation. She was so conflicted, because half of her wanted to run away, not feeling confident enough to approach the skeleton who was definitely-- if not, more, heartbroken than she was. But then the other half wanted to run to him, to talk things out with him, to plead him to take her back. 

"Just leave me alone, please!" Frisk sobbed, once again clenching her eyes tightly shut. 

"Mommy!" A small child's voice blurted, at least a couple of times, until Frisk finally opened her eyes, only to see Luna, sitting on her bed, within Sans' empty spot. She knew it couldn't have possibly been Sans, holding her hand. Instead, it had been her daughter, probably trying to shake her awake due to all the crying she was doing. "M-Mommy...? Are you okay...?" Luna asked, seeming scared that her mom was in trouble or something. Sadly laughing, Frisk sat up, trying to wipe her tears away. But they wouldn't stop. Why couldn't they just stop?

"D-Don't worry, Luna... Mommy is fine, I was just having a bad dream, that's all..." Frisk wanted to reassure her, to the best of her ability. However, for once, the girl who was easily swayed by her parents silly fibs, looked at her mom with extreme doubt. This was the one time that no one could fool her, especially not the woman who was currently crying, like her eyes were leaking waterfalls. She may have been a small child, but she wasn't always oblivious to what was right in front of her. "I'll be okay, so--" Frisk was saying, at least until the 6 year old suddenly tackled her mother into a hug.

"Don't lie, mommy! Telling lies is bad!" Luna blurted, while Frisk's eyes widened a little in surprise at her daughter, who hugged her tight. "I know you're sad! And that's okay! I'm sad too. You miss daddy and Leo, don't you?" Luna wondered, taking Frisk's silence as an answer. "I miss them too... But we can miss them together, so we're not lonely!" Luna suggested, in a happy, positive manor. Without a doubt, she took after Frisk, one hundred percent. Even if Frisk wasn't the happiest person she could be right now, it was clear to Frisk and even Sans, that Luna was most definitely like her mother. 

Just by Luna saying all of that, Frisk gradually began to break down even more, letting out harsh sobs as she finally wrapped her arms around her daughter in return. Of course, what was she doing? Why should she have to hide how she was feeling, when she was currently dealing with this heartache? She didn't normally like to hide how she was doing, she just wanted to think of the well being of her daughter. But if her daughter really seemed like she was okay with letting Frisk let out her emotions, then maybe she should just do that. Luna only continued to hug her mom, while she continued to cry, and cry, and cry... 

Eventually, Frisk did seem like she was slowly drifting off to sleep once more, and Luna sadly smiled towards her mom, who she knew was going through a lot right now. No, she didn't really totally understand everything that was happening, (seeing as she was unaware of the Mafia), but she wanted to help her mommy while she was sad. While Frisk had drifted off to sleep, the small girl tried her best to make sure Frisk was all tucked in and cosy, beneath her bed covers, while trying her best not to wake her up again. When that was all done and dusted, Luna thought of going back to her own room, only to decide against it, and instead, she decided to join her mom beneath the covers, snuggling close to her, in the hope to keep Frisk company, before closing her own eyes to try and fall asleep. 

She didn't want her mommy to be lonely.