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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He could do this... He could do this... Couldn't he? 

Never did Sans imagine that it would ever be this difficult to face Frisk, after having argued with her. Before, in the past, before he had even realised how he felt about her, facing her had never felt this awkward, when they had fallen out. Even after he had shot her down after she confessed to him, he hadn't felt as weird as this. Maybe because back then, he didn't know that he was crazily in love with her, and he didn't fear losing her forever. Slowly, he did raise his fist to the front door, only to hesitate, causing his clenched hand to hover before the door, rather than instantly knocking. 

"...Dad?" Leo lightly tugged on Sans' sleeve, to snap him out of his thoughts. "Are you okay?" He asked, wondering if maybe this was too much for his dad to deal with. Even he was feeling a little nervous to see his mom, but he had the slight feeling that Sans was a million times more anxious than he was. Sans looked down towards his son, giving him a small smile, and a nod, to try and reassure him that he was okay. Truth was, he was scared. But he wasn't going to outright admit that. Sighing, Sans finally did what he had set out to do, and that was knocking on the door, before stuffing his hands into the pockets of his hoodie that he was currently wearing. He hadn't actually changed clothes since they left, seeing as he didn't bring any clothes with him. He had kind of just rushed out the front door, that he hadn't really thought about that. 

The time it took to wait for the door to open, felt like an eternity, an eternity that caused the skeleton to grow all the increasingly more nervous. He almost thought of backing out, at least until the door began to open. "He--" The human on the other side of the door started, seeming to be on her way to say the word 'hello', but only the first syllable left her lips, when she spotted exactly who was standing on her doorstep. For a split second, she had to blink her eyes, as if she didn't believe it. "S-Sans...?" Frisk stammered, and glanced towards Leo. "Leo...?" 

"H-Hey mommy..." Leo murmured, nervously avoiding her eye. "I-I'm sorry... For leaving... I was just upset with you... But I'm... Well, I'm still mad, but I'm less mad now... I h-hope you're not angry at me f-for..." The small boy was saying, at least until he let out a small squeak of surprise, because he found himself pulled into a hug by his mother, who had knelt down to hug him close. She had even began to sob. 

"I'm not angry... I'm glad to see you.... I really am." Frisk cried, giving Leo a light squeeze, causing Leo to want to join his mom in sobbing too, as he decided to hug her in return. Sans stood, watching the two quietly, as he didn't know what to say. He didn't want Frisk to get the wrong idea, and to think that he was here to kiss and make up. Because he wasn't. He just... Wasn't ready for it right now. He didn't feel like he could handle it. 

"i uh... was just droppin' him off, so..." Sans trailed off awkwardly, glancing elsewhere, as he found it hard to allow his eye to meet hers. Frisk looked up towards the skeleton, seeming ready to speak, that was until Luna was excitedly bounding towards them from inside the house, happily exclaiming for her father, who she asked to pick her up. With a small chuckle, Sans did just that, causing Luna to let out a giggle as she wrapped her arms around her father's neck in a hug.

"I missed you! Are you coming back home?" Luna wondered, only to cause Sans to frown slightly, as he went to put her down. He didn't really know what to say to that, because he hadn't been planning on that today. He didn't want to seem like that he didn't want to spend time with his children - he did. He missed Luna a lot. But... 

"I think he's just visiting for today, sweetie..." Frisk lightly told Luna, ruffling the girl's hair, as she had to bite back her own disappointment that Sans likely wasn't here to stay to talk about things. Luna let out a small "awwwh" of sadness, and went to go back inside. "Leo, why don't you go keep your sister company?" Frisk wondered towards Leo, who nodded a little and went indoors. When the children had left, Sans and Frisk were both left in agonising silence, almost as neither of them knew who should talk first. 

"anyway... i was just here to bring leo home, so..." He had no idea what to say. He was almost ready to turn away, but Frisk stopped him.

"W-Wait." Frisk spoke. "I... Can we talk, please?" Frisk pleaded, staring back at the skeleton with pleading eyes. The skeleton found it difficult to look directly at her though, knowing that if he did, he might just break down. He sighed, not saying anything, but for some reason, Frisk took that as a queue to continue talking. "I'm really sorry... I'm so, so sorry, Sans..." Frisk spoke softly. "I... I really want you to come home... I... I miss you." Frisk said, fiddling with the rings upon her finger, which caused Sans' eyes to draw towards that, seeing as he could see the movement from out of the corner of his eye. 

"look, frisk... for as long as ya are part of the mafia, i can't." Sans shook his head. "i'm sorry... but i can't. it's too much." Sans muttered on, really fighting back the urge to cry. His pupils trailed back towards the ground, as if it was the most interesting thing in the world to stare at. At least this way, it was a tiny bit easier to avoid crying. "i can't keep havin' the same arguments, over and over again... i can't keep constantly fearin' the thought of ya dyin', or the thought of ya missin' important shit." Sans went on. It was too stressful. He knew he would feel so much better if Frisk just went back to her cafe job, if she would even be able to get it back after having quit. 

"...Are you not coming back to the Mafia then?" 

"no." Sans said, not even needing to hesitate saying that. It was funny, how at one point in his life he had been so, so scared if he didn't have that job. It had felt like being in the Mafia was a huge part of him, considering it was what he spent years of his life being a part of. It was how he met Frisk. But you had to move on someday, you had to try new things. He had no idea what he could do as another job still, but he knew that being in the Mafia wasn't his thing anymore, not with Frisk running the joint. 

"I can't just quit, Sans... You understand that, don't you?"

"it doesn't matter..." Sans stated. "...don't think, that just because i refuse to be with ya when you're part of the mafia, that i don't love ya anymore. because i do. i adore ya." He admitted bluntly, continuing all the while to avoid her stare. "but i just know that it wouldn't be a happy relationship if we can't agree on certain things..." 

"You know I love you too, right? I really do." Frisk replied, really beginning to sob, which was making it a million times fucking harder for Sans not to crack. The skeleton clenched his hands at his sides, really fighting back the tears. But hearing Frisk sobbing, and saying such things, made it impossible not to get set off. So, there he was, crying with her, as he didn't know what to say. 

"i know..." Sans replied. "...good luck with the mafia... and i'll probably... drop by every so often to see the kids anyway..." 

".....Okay..." 

Sans slowly nodded, causing silence to befall the two of them once again. With a small, and awkward nod, the skeleton decided that he should take his leave. Again, Frisk almost thought of stopping him from walking away, to get him to stay, but when she reached out for him, and opened her mouth to speak... She simply stopped herself. It was no use. As long as she was the boss of the Mafia, Sans wouldn't want to be with her. Could she really blame him? Not really... She did so badly want to give him what he wanted. She really did. 

But she couldn't. 

She just couldn't.