Steven doesn’t want to hurt anyone else, so he tries just pretending everything’s fine so that at least people won’t worry about him. Guess how that turns out.
The first one he talks to upon warping back from Homeworld is Connie, because evidently she’s been trying to call him for a while.
Connie: How are you?
Steven: I’m great! Never been better.
Connie: Really? Have you had anymore issues with swelling and glowing pink?
Steven: Um…nope? Well, maybe, but how about you? How’s college prep?
Connie: Steven, it’s fine, but what do you mean maybe?
Yeah, he can’t get much past Connie. Unless he finds an excuse to hang up on her.
On the one hand, he didn’t even realize he’s been glowing this whole time, but somehow I doubt that would’ve changed his conversation with Connie much.
Steven: No, no no no no! This isn’t happening! I didn’t think about shattering White, I didn’t shatter Jasper! I didn’t fight with Dad! I-I’m Steven Universe! I’m fine. I’m fine!
And now he’s just (accidentally) shattering glass left and right, and as such he finally alerts the Gems of his presence.
Pearl: Are you okay?
Steven: I’m fine. Going to see the Diamonds was a waste of time. I thought I needed to figure myself out, but I know who I am! I’m Steven Universe! I help people, I don’t hurt them.
Amethyst: Dude, what’s going on? You look really different.
Steven: I’m still good old Steven!
Garnet: Steven, we’re worried.
Steven: I’m okay. Really!
Garnet: We’ll take your word for it.
Then he runs off to Little Homeschool (literally) before they get the chance to ask any follow-up questions (like “How was Homeworld?” or “Seriously, what’s wrong?”)
Thus begins the portion of the episode where Steven tries to act like nothing has changed but everything has changed and he has no control over his power so he just makes everyone miserable when he tries to “help” them.
Long story short, he accidentally demolishes a sizable portion of Little Homeworld.
Steven: Uh, oh, I’m sorry. That was an accident. But, what are accidents other than new opportunities to improve, right? We all make mistakes, and as long as we improve ourselves, everything is going to be okay!
It’s pretty clear that he doesn’t really believe that by this point.
But at least he gives them enough time to arrange a family meeting. Including Connie, who received a literal call for help from his subconscious on her phone, as you do.
Connie: I can tell something is bothering you.
Steven: I don’t know what you’re talking about! I’m fine – awesome, in fact. Come on, you’ve seen me when I wasn’t doing well.
Greg: Steven, if being like this is what you want, then we’ll support you 100%, whatever makes you happy. But if you’re not happy, if something’s wrong-
Steven: Nothing’s wrong! Besides, I don’t want you to worry.
Connie: We are worried!
Protip: If you don’t want people to worry, don’t tell them you don’t want them to worry, because that always means there really is something to worry about. As evidenced by the way they instinctively block the door, since he’s run off on them at least twice by now.
Greg: Steven, you know you can tell us anything.
Of course they’ll listen to anything he has to say, but that doesn’t mean nothing he says could change what they think of him – and that’s exactly what he’s scared of. But Connie starts off by informing the Gems about his trip to the hospital (since he never told them), and once he starts talking, it’s hard to stop.
Steven: Have I done some things wrong? Sure! I trashed the house today, I broke an anvil – what teenager hasn’t? Dad and I had a little disagreement – that’s practically a rite of passage! I mean, it would be weird if we didn’t, right? And maybe I’ve had a not so nice thought or two about, you know, slamming White Diamond’s head through a pillar, but it’s not like I actually went through with it! I only actually shattered Jasper!
Connie: You’re joking, right?
Steven: Oh, don’t worry! I fixed that, too! I can fix anything! I can just keep messing up and fixing things forever, and you’ll never have to know or think about any of it!
Steven: How messed up is that? That I’ve gotten away with this for so long…you have no idea how bad I am! You think I’m so great, I’m so mature, and I always know what to do, but that’s not true! I haven’t learned a thing from my problems. They’ve all just made me worse! You think of me as some angel, but I’m not that kid anymore! I’m a fraud. I’m a fraud…I’m a monster!
Steven’s been the heart of the Crystal Gems at least since Season 1, so he eventually concluded that they would fall apart without his infinite emotional support. That alone is a horrible burden for a kid, but add to that all of the serious trauma that he faced, and it’s not so much a question of why he’s breaking down now, but how he managed to hold up as long as he did. He’s not a monster for having negative feelings, but he’s been ignoring them for so long that he simply doesn’t know how to process them.
Until next time…