The CGs probably have a lot of resentment towards Greg after Steven was born. It's important to remember that Rose was probably the most important person in their impossibly long lives. Getting back at the person who took her away probably felt good even if it felt terrible at the same time. Greg even yells back at her that he can't let her do this again, so the implications of whether or not "something" happened between them happened holds some weight especially if this was just after Rose's passing where Greg was at his most vulnerable and Amethyst at her most lonely/angry.
Of course this is one of the most awful things anyone can do to someone. Even Amethyst realizes what she's done by the look of her face and running off without saying a word after Steven shows up. But Amethyst is a good person deep down but probably harbors a lot of dark thoughts about herself and others but keeps it to herself all the time. I wouldn't be surprised if Amethyst herself hasn't forgiven herself for this or many other things she's done. But there goes Greg forgiving her just like that. Even when >>86261866
pushes him off a roof, he still forgives her. Shows how good of a person Greg is and probably why the CGs don't show outright animosity towards him.>>86258766
What I found most interesting during that whole scene is that Pearl calls Steven Rose.I honestly think Steven absolutely hates being called Rose because that removes Steven's own identity as a person and nullifies his own deeds. So having one of the four closest people in your life break that unspoken rule would hurt immensely let alone almost letting him die. Then again that's just how I see it.