Tony Stark should have died at the end of the first Avengers film.
The final scene saw Iron Man take a nuclear weapon through an alien wormhole, detonate it in the middle of a pan-dimensional army and then, by luck, fall back down to Earth where he was caught by the Incredible Hulk. It was an act of self-sacrifice, as well as an answer to Captain America's earlier criticism of Stark's selfishness.
Stark didn't die, because heroes with that much star power can't die in films based on comic books. But the writers of the ensuing movies have been increasingly showing the strain that his survival has put on his mental health.
This was a major theme in Iron Man 3, with Pepper Potts struggling with the act of supporting Stark. She doesn't do a great job, but who would? Dealing with a partner who is struggling with anxiety and, arguably, PTSD in your relationship is hard enough for normal people, and that's before you get involved with someone whose symptoms include a pathological need to make technology that has the potential to kill you when he has a bad dream.
All that being said, I would still argue Potts often comes off as dismissive and, as we know from Civil War, the relationship ultimately ends.
Stark actually does try to reach out and tell someone about all this, but unfortunately Bruce Banner falls asleep during the session shown in Iron Man 3's post-credits scene. He also states he's not "that kind of doctor," and fair enough. But he should be able to listen to his friend and maybe provide a referral?
These characters are told and shown over and over again that Tony Stark is struggling in real, profound ways, and yet no one thinks to ask for the proverbial keys for the Iron Man suit for a week or two while he talks to a professional? Things only get worse as the movies continue.
The Scarlet Witch's vision from the second Avengers film was only able to unsettle Iron Man so profoundly because of his these unresolved feelings. He wants to wrap the globe in a sort of anti-Thanos condom to keep everyone safe, and that leads directly to the creation of Ultron.
The narratives of these films loop around each other fairly often. Stark was first asked to hand over the technology behind the Iron Man platform in the second Iron Man film, and refused. The idea of a fist wrapped around the planet was first seen is Captain America: The Winter Soldier, and Steve Rogers both rejected the concept and ultimately found the project was under Hydra's control.
The creation of Ultron may have been Stark's attempt to give himself enough room to take a breath, but it led to worldwide crisis and ultimately a nearly world-ending battle in Sokovia, the fallout of which is picked up in Captain America: Civil War.
Everyone assumes Iron Man will be fine
What's interesting is that Stark is the only Avenger who seems to be struggling with his mental health in a way that shows so openly that he needs help from a professional. Banner knows he can't be trusted with his own power and has disappeared. Steve Rogers has begun to open up to his friends and seems much more comfortable in the present day. The Captain also seems happy to have Romanov's support when Peggy Carter passes away. Multiple characters are shown checking in with Wanda Maximoff to make sure she's processing what's happened.
Other characters are struggling, but they're struggling in ways that seem to suggest they'll ultimately learn how to deal with their feelings and they have the support and love they need. Everyone assumes Iron Man will be fine, and that neglect is part of the reason we see him getting worse throughout the films.
Tony Stark is a man who spent $600 million to come up with a way to work through the death of his parents with technology. He's jumpy. He complains of pain. He becomes so frustrated with his inability to express himself that his head darts around, searching for the right words.
He may frame the situation as wanted to be kept in check by the UN, but the reality is that he's screaming the words "help me" to everyone around him, and no one is listening.
Potts has left, his collection of Iron Man suits has been destroyed and he's alone after having caused multiple terrible situations. Situations that, in fact put him in fight-or-flight battles that likely exacerbated his still-untreated mental health issues from the previous films.
We see situations where Steve Rogers is sensitive enough to know footage from Sokovia is hurtful for Wanda, and she's given time to heal and learn, but everyone in Stark's life reacts to his ongoing struggles with antagonism or abandonment. Of course he's hitting rock bottom and feels backed into a corner: Stark is having an increasingly impossible time processing his own trauma while continually being put into violent situations as the direct result of his own attempts to work through his pain.
"Tony’s struggle with anxiety is poignant because it allows us to realize that he is, in fact, still human," Dr. Andrea Letamendi, a clinical psychologist, wrote back in 2013. "To this end, it doesn’t matter to me if his panic attacks are indicative of clinical PTSD, complex PTSD, subclinical anxiety disorder or another psychiatric category we can use as a label. The point is this: A brilliant, powerful, and tough guy can be vulnerable, scared, and confused. Tony Stark is a superhero with the psychological makeup of a human."
This is all interesting stuff, and the writers and directors of the Marvel cinematic universe continue to look into this aspect of Stark's character for richer stories and a more human tone, but it's frustrating how many times he's reached out to those around him and they don't seem to see how badly he's suffering.
Captain America: Civil War is framed as a battle between Captain America and Iron Man, but it's really a war between Iron Man and his own demons. Loki is the only existential threat the Avengers have faced. The rest of the problems they're forced to solve have been caused, directly or indirectly, by Stark's own attempts at "fixing" himself.
It's not even that Stark hasn't asked for help in the previous films. He has, multiple times. But those around him, until the final monologue in Civil War where Rogers promises to be there for him, don't seem to have been willing to listen.
And it's costing everyone dearly.