Now has never been a more perfect time to answer a question of this nature.

Before I end up most likely writing an essay though, someone else asked a somewhat similar question, specifically about whether Childe is happy, and if he's content with his isolation. Since both of your questions would have similar responses, I figured it'd be a great idea to address them all here. So let's hop to that!

Firstly, this response will contain spoilers from Mizuki's story quest. If you haven't played it, I wouldn't recommend reading this yet. But if you're okay with spoilers, then you can disregard this.

In Natlan's interlude AQ, we get a small look into the effects of the Abyss on the Natlanese fighters. Many were experiencing severe trauma, hallucinations, and intensified negative emotions such as grief and feelings of worthlessness and/or helplessness. This is because the Abyss preys on the weaknesses of the individual, as we witnessed with Kachina's situation. The Abyss Lector stalked her throughout the Night Kingdom, attempting to break her down by capitalizing on her worst fears and darker thoughts.

Now, we have Mizuki's story quest, which does a stellar job at exploring emotion, the connection between them and nightmares/dreams, and the importance of negative emotions. In fact, it covered many things that a friend and I had already been discussing together extensively, so we were very excited about this quest prior to its release.

In any case, Mizuki's quest emphasizes the danger of suppressing your emotions, as well as the effects that this can have on the human subconscious. If this is left to fester, then these suppressed emotions will manifest as nightmares. However, these emotions are not inherently a flaw. All of our feelings—sadness, anger, fear, etc—are a part of our identity. We aren't solely our pain and suffering, no, but that pain and suffering is an inextricable piece of us. It can determine our dreams and goals, it can help us grow and learn, it can foster empathy and compassion. Pain is part of being human, and pain can be our strength.

The division on the topic of Childe's trauma and overall psychological state is understandable; after all, much of our characterization in this area comes from observation, interpretation, and our own headcanons to fill the spaces that the story has yet to fill. But I believe this division stems from more than simply lack of canon information. It is partially that, but I also believe it to be this: there are people who have created a strong, infallible version of Childe in their heads.

This is not necessarily a bad thing, because it's exactly what the writers want.

What I find fascinating is that the perception of Childe in the story, and the perception of him by an overwhelming majority of the fanbase, is shockingly similar. He is heavily underestimated, disregarded, isolated—but most of all, his humanity is seldom taken into consideration, his strength and role as a weapon heralded above it and all else.

Take Fontaine for example, where it quickly becomes apparent that this is a serious, and even deadly issue. Most of the characters involved in the investigation of his disappearance were more perplexed than concerned, ultimately convinced that he was more than capable of taking care of himself. While this confidence can be positive in a different context, it is primarily detrimental to Childe. It served as an example that he lacks human bonds and connections, that so long as his image is a competent, strong character, other characters will feel little urgency to help him and provide support. And this lack of support nearly resulted in his death, a month-long battle of survival with only himself to rely on.

And this is absolutely a purposeful narrative decision. Note how in each region's AQ the Traveler has never truly fought a battle by themself. In Mondstadt, they had Diluc, Venti, and Jean in the fight against Stormterror. In Liyue, it was with the Qixing and the Adepti. In Inazuma, it was with the numerous wishes of those who sought to abolish the Sakoku decree, as well as Yae Miko's advice and intervention. In Sumeru, it was Nahida and the collective wisdom of the people. In Fontaine, it was with Neuvillette. And finally, in Natlan, it was with Mavuika, the six other chosen warriors and the souls of the dead. The key themes in Genshin, and mostly all of Hoyoverse's games (unsure of ZZZ as I have not played it), have always been the right to choose your own fate, and the importance of humanity coming together.

Childe, who is the "pawn" as he has described himself, lacking in any bonds/connections, is essentially being used by the writers to explore and demonstrate the consequences of not having these bonds. Can a person truly fight alone? The juxtaposition between the Traveler and Childe's positions in the story is a result of the writers answering this question. And so, for that reason, Childe is alone. But is he lonely? Does this isolation affect him to a degree? And if so, how? Is he truly happy?

This is where an extremely crucial detail comes into play: Never-ending Performance.

I've mentioned this in the past, but this is a much, much more important detail than it is given credit for. Not only is this the title of one of Childe's boss themes, but it is also the title of Kaeya's second constellation, and a phrase similar to it, "endless performance," is used when describing Furina's role in tricking Fate and saving Fontaine from the prophecy. However, this isn't solely about the phrase/concept itself, but about the characters it is attached to.

Kaeya is implied to be a lonely, and even depressed character. He does not have a sense of belonging in Mondstadt, and tends to hide his true personality under a mask of confidence. The calm, collected, outgoing and charming Favonius knight is, in reality, actually a shy and reserved character struggling with his past and his loneliness. Even Razor, in the past event "Of Ballads and Brews, describes Kaeya as the "...Grown-up with the fake smile," (and I never could forget that). And Furina, as we had seen in the Fontaine AQ, had to put on a "performance," pretending to be the Hydro archon, smothering her true self for the sake of her people, crying alone and forced to carry a heavy burden by herself with no one to turn to. And in one scene, she hadn't even realized in the moment that she was crying. This five-hundred year performance left her exhausted and traumatized, to the point she nearly walked away from the stage for good, until she made the decision to take the stage once more and received her Vision.

Note how both Furina and Kaeya have both experienced extreme loneliness. They don a particular persona, hiding their true feelings and massive secrets from others. While Furina was eventually freed from the "performance," the same cannot be said for Kaeya. And additionally, the same cannot yet be said for Childe.

By drawing thematical similarities between these characters, we can, by extension, draw a similar conclusion for Childe. He too is in his own never-ending performance, presenting different masks to different people. For his siblings, he is the "bestest big brother" and the "toy seller" for Teucer, and for the sake of diplomacy he is the friendly and charming "Childe," but he is also "Tartaglia". He is the weapon of the Tsaritsa, he is unpredictable, he is chaos. And all of these identities are simultaneously separate and melded into one. But I believe he ultimately seeks companionship. He simply has not been given the tools to do this in a healthy manner.

Back in the Liyue AQ act 3, Childe says this: "Anyone who strives as I do to grow stronger shall be called a friend, even if our friendship can only be shown in battle against one another."

Believe it or not, this quote is actually just one example of how Childe's time in the Abyss affected him. And more specifically, the time he spent training with Skirk.

In the Fontaine AQ, we learned that Skirk spoke very little with 14 year old Ajax due to his not being strong enough, and even in Arlecchino's story quest, he says, "...Unless Master feels the need to meet with me, she's not going to be found. But, that problem has an easy fix. I just need to become stronger..."

This is someone who ties his self-worth to his strength, who seeks connections through battle. Every request for a spar is a request for human connection. It's quite literally become his own language, and the one he is most confident in. If he's strong enough, then the people he admires and/or seeks to befriend will acknowledge him. This sentiment applies to Skirk, to Capitano, to the Traveler—to anyone he sees as a potential friend or an admirable figure. And this is because everyone in his life has particular expectations for him, because nearly every relationship has been formed based on his strength and his usefulness. Even Pulcinella had been drawn to him because of his strength. And his pursuit for strength in and of itself was because of the Abyss.

This isn't just coming from the parallels between him and Chasca, who was marked by the Abyss, but also because of the very conditions of the place itself. He was a 14 year old with a timid disposition and no experience in combat, forced into a position where he had to fight to survive in a dark, unfamiliar environment crawling with all manner of otherworldly creatures. His only choice was to fight or to die. But because of his desire to be seen as a strong warrior, Childe does his utmost to hide his more vulnerable side. He doesn't want to be seen as weak, he doesn't wish to be pitied—because if it ever came to pass that he was deemed as weak, what else would he have left? Without his strength to bridge the gap between himself and other strong fighters, what would he do? What would he be?

TLDR: Childe is not as happy as he appears, is not necessarily content with his isolation because he frequently seeks out human connection via combat, and has indeed been affected by his time in the Abyss as displayed through the aforementioned social behaviors.

End note: If you'd like a thread that further dissects Childe and his relationship with his past, I highly recommend my good friend Lucian's thread. He does a magnificent job analyzing Childe's behavior down to the letter, from the subtext in Childe's words to his micro expressions. Here's the link: https://x.com/wormlandalice/status/1779058365261398296

(I really wanted to add even more moments to this ridiculously long essay, but that would've just been...even more lengthy. Even this is way too long lmao)

Anyway, I hope I was able to answer both you and the other anonymous narwhal's questions well! Even if this was way too long. And I hope that I was able to provide at least some insight into Childe's character and his hidden struggles, because it's truly a topic near and dear to me.