The entire existence of the MCU Tony has been overcome by fear. Fear that one day he might not be able to save the day. Tony feared that people were not doing enough to stop the 10 ring terrorist group in the first Iron Man film so he became Iron Man, when he was dying he was terrified of death so he tried to ignore his fear by escaping into the bottle in Iron Man 2. In the Avengers, Tony goes into the worm hole to save the planet from the Chitari Invasion.
In Iron Man 3, we see Tony suffering from PTSD and overcome by fear of failing. In Avengers Age of Ultron, Tony is shown a vision of the Avengers all dead and cap says its his fault Tony is terrified of this and out of fear he creates Ultron who leads to many deaths and the rampage The Hulk went on.
That rampage will probably have a big impact on the governments registration act in [Captain America: Civil War](tag:994409), of course Tony will jump right on that out of fear yet again of what the country would be without it and this leads to him and Caps battling. Eventually i assume Cap will surrender and be killed similar to in the comics. Tony would be so distraught over Steve's death that he would retire the suit and go into exile. Just in Time for Avengers: Infinity War Part 1 the Avengers now leaderless prepare to go up against Thanos when Cap finally returns to lead the team with Tony still gone the team goes up against Thanos and loses getting slaughtered by him and Tony returns to see them all dead except for Cap who asks why he wasn't there. Fulfilling that vision Scarlet Witch had shown him all those years earlier.
Tony quickly unites the heroes still remaining, the ones who wouldn't fight alongside cap and those introduced in phase 3; Black Panther, Stephen Strange, Captain Marvel, Spiderman (who just like in the comics eventually sides with cap during Civil War, but who Cap refused to take with him during the battle with Thanos because he was still in high school. Tony on the other hand has no problem with Peter's age so he lets him join.), they go up against Thanos and get beat up before he finishes them off, 70s music starts playing and the Milano lands and the Guardians jump out and then suddenly and einstein rosenbridge opens up and Thor, Hulk, and Loki appear and join the fight the knock back Thanos and Adam Warlock shows up and rips the Guantlet off his hand and uses it to revive Cap's team. Adam leaves with the guantlet and Captain America, Iron Man, and Starlord, unite the 3 teams to take down Thanos. After the battle the team discovers Adam Warlock has gone mad with power and all of them work together to stop him before once again separating the stones to the far off reaches of the galaxy after getting each others contact information.