Prompt of the Day - 4/15/19 holidaysat221b: After the events of TFP, Molly and Sherlock get closer. Suddenly, though, he pulls away and starts flirting with a coworker of hers, sometimes blatantly in front of her. It isn't until an event at Barts that the truth comes out that it was all for a case. - noregretsnotearsnoanxieties

A/N: Title taken from Billy Joel's song by the same name. Rated T for some bad language on Molly's part. Which she is totally justified in using, by the way.

Good, good, Molly had come to the Bart's fundraising event as planned, and her blackmailing coworker had been quietly led away by the Met, also as planned. And now, finally, he could take Molly into his arms and dance with her - also as planned.

Well. So much for plans.

Molly gave him a cold stare as she stood before him in her sparkling red ballgown, arms crossed in classic defensive - angry? - posture. "You've treated me like shit all week, Sherlock, while making a spectacular ass of yourself with Whitney, so what makes you think I'll just fall into your arms like nothing's happened?"

His brow creased as a feeling of unease crept up his spine. Why was Molly being so...not her? The case was over! And this open ballroom wasn't actually the place to have this kind of conversation, he didn't need a Mind Palace John Watson to tell him that. At least Molly willingly accompanied him as he led her to a secluded corner on the opposite side of the room.

"Whitney's been arrested, you know I was just flirting with her for a case," he explained as he studied her stiff, unhappy form. How could she not understand? His unease was rapidly heading toward panic as Molly's expression softened not one iota.

"A case?" she said, with something very like a sneer in her voice. "So, what, like with Janine?"

Sherlock nodded warily. "Of course, how could you not know that? I said I had that blackmailing case to…"

"So did you sleep with her too, like Janine?" Molly interrupted. "Take showers with her, or maybe baths - John wasn't very clear about which one you two shared that time," she added, her voice even colder. "Did you make out with her, put your fingers in her tw–"

"No! No, nothing like that-and I never slept with Janine!" Sherlock exclaimed, shocked at her words. At how - angry? Yes, definitely angry - she was. Molly was the one who was supposed to understand all and forgive all - except when it came to drugs, of course, she'd made that VERY clear. No drugs for cases, no drugs for ANYTHING, Sherlock, or we're through. I love you but I can't watch you go through that again.

That had been the only hard 'make or break' rule she'd laid down, to which he'd more than willingly agreed. So why was she so angry about this? "I didn't do any of that... stuff. Just a little harmless flirting," he tried again, but Molly raised her hand, stopping his attempted explanation.

"There's no such thing as harmless flirting when you don't tell me about it first," she said. "I'm not John, Sherlock, you can't just assume I'll go along with whatever nonsense you've got going on, that you don't have to explain things to me, like I'm, I'm nobody to you!"

And now it wasn't just anger in her voice, it was hurt and humiliation - how would Eurus put it? All those complicated little emotions, I lost count. This time it was him losing count, now that he was really reading Molly, deducing her the way he tried so hard not to do in case it hurt her.

Well, he'd hurt her anyway. As he'd always known he would. "I'm sorry," he said, knowing the words weren't enough. "I just assumed you'd understand. That I had to act like we were going through a rough patch - I thought you were just playing along. I'm sorry," he said again.

Molly nodded, her face expressionless. "Fine," she said after a moment, her tone of voice telling him how very not fine she actually was. "I accept that. But." She moved closer, closer, crowding into his personal space in a way he usually enjoyed but not so much today as she thrust her face up towards his aggressively. "If you ever do anything like that again without telling me what's going on, I. Will. Leave. You. And maybe that's not much of a threat to you since you and I are so new…"

He couldn't help himself; he caught her hands up in his and met her eyes, hoping she could read the desperation in them, the truth in them, as he said, "I swear, Molly, I swear to you, I'll never do this again. Not without explaining things first. Because that threat…it's the worst thing you could do to me. I thought I could live alone and do just fine without friends, without…without someone to love the way I love you, but I know that I can't. I need John, I need, Mrs. Hudson and Lestrade and even Mycroft and my parents and Eurus; I love them, even, but not the way I love you. You mean the world to me. I never understood that phrase until the day I saw a coffin intended for you, and almost watched you die. I love you. And I will try very hard never to hurt you like this again."

He leaned his head down so that his forehead rested on hers, surprised but not shocked to feel tears gathering in the corners of his eyes. Then he felt the soft pressure of Molly's thumbs as she wiped them away, felt her move beneath him so that he could rest his head in the crook of her neck and feel the warmth of her arms as she gathered him in close, and understood without her saying so that she forgave him.

This time.

And as he hugged her so tightly she murmured something about needing to breathe, he made a private vow - so much for the one he'd made to the Watsons at their wedding being his last! - that there would never, ever be a next time.