Maximum Capacity is an episode centering on Amethyst and Greg (and Li’l Butler, of course, but that hardly needs to be mentioned); it’s not the kind of episode where we find clues about the conflict in the past or hints about the coming storm.
There’s one big character-related issue to talk about, however, so we’ll spill some pixels on that.
They’d better not be watching that dumb show
The timeline of Amethyst’s and Greg’s friendship is open to some interpretation, but we have a fairly good picture of it. We get the impression that after Steven’s birth they would watch Li’l Butler together for days at a time for quite a while; Greg mentions they watched them a lot when Steven was little, indicating a good amount of time, and Garnet and Pearl likewise talk as though this went on for a while.
There’s no explicit indication of when exactly the friendship started, but it seems that the binge-watching of Li’l Butler only started after Rose Quartz gave up her physical form; both Amethyst and Greg had lost someone very important to them, and Li’l Butler offered them a way to forget. Amethyst in particular seems to have the poor coping skills that would make such an escape particularly desirable.
Matt Burnett gives the indication that the friendship did in fact predate the loss of Rose, which makes sense. Surely Rose would have introduced her friends to her beau, and Amethyst and Greg are kind of a natural fit; they certainly have similar taste in television.
I bet you’d stay for her
One day the friendship between Amethyst and Greg abruptly stopped. Judging from Greg’s response to Amethyst shapeshifting into Rose, the final event involved much of the same: Amethyst using Rose’s form to mess with Greg’s head.
There was probably a hefty amount of intermittent abuse from Amethyst before then: even years after the loss of Rose, Amethyst was still using emotional manipulation to keep Greg with her and parked in front of the television so she could have a watching buddy.
Amethyst’s emotions towards Greg seem to be complicated: on one hand he’s her buddy, and a good person to hang out with. On the other hand, she seems to regard Greg as responsible for her emotional well-being. Whether she blames him for the loss of Rose or not, she certainly seems to feel owed his attentions; him saying he had to be there for Steven was too much for her to take, prompting an egregious step over the line.
Knowing how Amethyst is, without anyone to counsel her after she and Greg had their first falling-out she probably stormed off and stewed about it for a while until she basically forgot about it. This time Steven was able to give her the push she needed to realize she had to try to make amends.