At the end of Avengers: Infinity War, Tony Stark (Iron Man) is left in a state of immense grief, guilt, and shock. The film concludes with the devastating event known as "The Snap," where Thanos, the main antagonist, uses the Infinity Gauntlet to wipe out half of all living beings in the universe, including many of the Avengers' allies.
Tony's mental state is not explicitly explored in great detail in the film's closing moments, but based on his experiences throughout the movie, it is evident that he is likely to suffer from both PTSD and depression.
PTSD: Tony has experienced numerous traumatic events over the course of the Marvel Cinematic Universe (MCU), including near-death experiences, battles, and witnessing the destruction caused by powerful villains. In Avengers: Infinity War, he is shown facing a series of intense and emotional situations, including an encounter with Thanos on Titan, where he nearly loses his life and witnesses the demise of some of his closest allies. These experiences are likely to leave a lasting impact on his mental well-being, contributing to symptoms of PTSD such as intrusive memories, nightmares, hypervigilance, and emotional numbing.
Depression: The loss of his friends, especially the heart-wrenching demise of Peter Parker (Spider-Man) in his arms, adds to the burden of guilt and sorrow that Tony carries. The weight of responsibility for not being able to prevent the catastrophe, coupled with the fear of losing those he cares about, can lead to feelings of hopelessness and depression.
It is important to note that Tony's mental state at the end of Avengers: Infinity War sets the stage for his character development in Avengers: Endgame, the subsequent film in the MCU. In Endgame, the impact of the events of Infinity War on Tony's mental health is further explored as he deals with the aftermath of "The Snap" and grapples with his emotions.
Overall, Tony Stark's mental state at the end of Avengers: Infinity War is characterized by profound grief, guilt, and likely a combination of PTSD and depression due to the traumatic events he endured and the losses he experienced.