Post-HLV, everything is going right for John: he's still with Mary, and after a long discussion with her, he's also become romantically involved with Sherlock. He spends days running after Sherlock and helping track down Moriarty while constantly checking his phone, waiting for the moment Mary goes into labor.

It all happens seemingly at once: they take down Moriarty, and shortly after Mary finally gives birth to their daughter. Then, as soon as John has a moment to spare, he and Sherlock have sex for the first time.

And then it all spirals out of control — for John, anyway. He's exhausted with the new baby, but every time he's not caring for her, he's at Sherlock side, and if they aren't pursuing a new case, Sherlock is insatiable. Mary may not be quite so hungry for it, but she certainly wants sex, too. He can't even think about his job, and how he'll have to return to it soon or be sure he can leave it and remain financially stable enough for the baby.

John's constantly out of energy trying to fulfill the needs of the three most important people in his life, but he's also so blindingly happy he can't bring himself to tell either Mary or Sherlock that he needs to slow down.

So what happens then?