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 didn't know if he would ever get used to it, waking up in the mornings and opening his eyes, only to be able to see his hand that had the engagement ring that Frisk had given to him sitting on it. Not that he was complaining. Matter of fact, all he ever did was smile widely, knowing that he was now actually engaged to his girlfriend. It wasn't like some crazy thing that he had dreamed up within his skull; it was actually happening. Somehow, now that they were actually engaged, the thought of them being married wasn't actually so scary anymore. Actually, he couldn't really remember what he had been so afraid of in the first place. 

"Morning..." Frisk murmured sleepily, cuddling close to the skeleton's back as she went to lightly bury her face into the side of his spine. He softly smiled, just feeling so content and calm after their simple, but enjoyable date last night. He decided to turn over so he was facing towards her, and he went to give her a light kiss. She simply quietly giggled into the kiss and kissed him in return, until he pulled away to grin at her perfect face. She slowly and properly opened her eyes to stare back at him.

"mornin', honey." He teased, instantly seeing Frisk beginning to blush bright red at the nickname he had chosen to suddenly give her. He had never called her "honey", in all the time that they had been dating. It did feel more like a nickname a married couple would give each other, which was why he jumped at the opportunity to say it, and her reaction was so worth it. "heh, you're so cute." He beamed, while she whined and covered her face with her hands due to her embarrassment. 

Though, the moment between the couple was interrupted when Frisk noticed the sound of her phone buzzing on top of the small desk beside her side of the bed. Going to remove her hands from her face, she went to reach towards her phone, while the skeleton continued trying to hold to her still, seeming quite clingy for this early in the morning. But who could blame him for being in a good, and romantic mood after the lovely evening they shared yesterday? When she went to look at what the source of the buzzing was, she saw that she had gotten a text from Asgore to come into work today. Sans was able to see the text from where he was laying and he let out a soft, disappointed sigh.

"can't ya stay home today? it seems like ya work more often than i do these days..." Frisk was actually probably asked into work a lot more than he was now. He knew that she had skills, but he had no idea that she would probably end up being considered better at his own job than he was... Not that he didn't care about not working as much, because he would rather put his living into his kids nowadays, over working for the Mafia. He never could have seen himself quitting the Mafia, not ever. But now with the life he had... Sometimes he did consider the idea. 

"It's my job though, Sans." Frisk told him, already seeming ready to get up, while the skeleton frowned. 

"i thought bein' a waitress was your job. why do ya need two?" He questioned, going to sit up as she was going to grab some clothes to change into. He didn't want to turn this into an argument after the nice night they had yesterday, and after they had just gotten engaged, but... It was something that was on his mind a lot of the time. Why did she still insist on working for the Mafia? Before, she shied away from the idea of murder and death, but now... Yeah, he had to admit that when he saw her kicking someone's ass, she looked extremely badass and sexy. However, at the same time... He was concerned about his worst fears coming true: that she would value the Mafia more, over him and their kids. 

"Don't start this again..." Frisk muttered, while Sans exhaled.

"i'm not startin' anythin'. it's just..." Sans trailed off. "...i just don't like how much of your time it takes up. and don't think it's me tryin' to boss ya around, because it's not... it's just..." 

"I thought you didn't have any problem with me being a part of the Mafia anymore, as long as it didn't get in the way of any important events." Frisk told him, crossing her arms as she stared towards him, and he couldn't help but narrow his eyes a little bit in return. "It's not like I'm gone for every second of every day. I think you're making a bigger deal out of it than you need to." She said. 

"i'm not makin' a big deal out of anythin'." Sans snapped in annoyance. "excuse me for wantin' to spend more time with ya. but turn this into a disagreement if that's what ya wanna do." He complained, going to lie back down and turn over onto his side, so his back was facing towards her, then he pulled the covers back over himself to give the obvious idea that he was angry at her now. He hadn't wanted this to be an argument, but if she wanted to be that way... She could just go to work if that's what she really wanted. For a minute, he had been sure she had gone to leave without another word when silence filled the room, however, instead, she climbed back into bed, going to hold him and kiss him at the side of his spine. He tried to ignore her, at least until she spoke again.

"You know that I love you. It's not that work is more important than you or the kids, that's not it at all. I just like being able to see all our friends again more often. And I like being able to help Undyne with things." She told him softly, while his pupils stared towards the wall as he was listening to her words. He exhaled, knowing that she did mean well. She wasn't an awful person, and it wasn't like she was purposely going out of her own way to bother him. He wasn't trying to control what she was doing, because in a way he didn't really have any right to tell her what to do. 

"...i know... i love ya too..." Sans replied, going to turn back onto his back so he could look towards her. She gave him a warm smile, which was so contagious he could only smile back. He went to carefully wrap his arms around the back of her neck to pull her close and pull her into an affectionate kiss. If anything ever showed how much they loved each other, it was definitely moments like these, where words weren't even needed. Sans really wished he could keep her here right now, that she would just stay home with him as he quietly groaned into the kiss, at first from the enjoyment of getting to kiss her, but then from the disappointment when she began to pull away. 

"I'm sorry, but I really have to go." She pouted. "I'll see you later, okay?" She told him, giving him a quick peck, and that's when she bolted out of the room to get changed, before she would be going out of the door to head to work. Again, he sat up with an exhale of breath, definitely down about the fact that she wouldn't stay at home. It was different when she went to her cafe job, because he knew she had to go to that job. But no one was forcing her to work for the Mafia, not even Asgore despite asking her to come in. He could have probably easily found someone else to take her job for her. 

But he just had to remember not to get the wrong idea and think that she was choosing her job over him. If that had been the case, she wouldn't have wanted to propose to him, would have she? Looking at the ring on his finger once again, he began to fiddle with it a little as a small smile did manage to slip across his mouth. He had to remember that he was special to Frisk, just as she was to him. If she enjoyed her job, then he shouldn't be the one to take that away from her. Just as long as she still didn't let it interfere with the lives of their kids. 

Then he was fine with that.