Well, it could be that Steve had been influenced by outside forces. For example, if there was some sort of mind - control or misinformation that made him act against Tony. And then when he realized the truth, he had to apologize. Also, Steve might have been too stubborn in his beliefs and not listened to Tony's perspective, and later came to understand that he was wrong and needed to say sorry.
One reason could be a misunderstanding during a battle. Maybe Steve made a strategic move that put Tony in danger without realizing it fully. Another might be that Steve said something harsh in the heat of an argument, like criticizing Tony's technology when it was actually saving lives. Or perhaps Steve made a promise to Tony and failed to keep it, which made him feel guilty and led to the apology.
Steve could be apologizing for a past betrayal. In some fanfictions, there might be a situation where Steve sided with someone who was against Tony, even if he didn't fully agree with that person. This act of choosing the 'wrong side' could have deeply hurt Tony. Additionally, Steve might have accidentally damaged something important to Tony, like his suit or his lab equipment, and felt bad enough to apologize.
One possible reason could be a misunderstanding during a mission. Maybe Rhodey made a decision that put Tony in danger without realizing it at first, and later realized his mistake. For example, if Rhodey called for backup in a situation where it attracted more enemies towards Tony. Another reason might be something related to their personal relationship outside of the hero stuff. Perhaps Rhodey said something unkind about Tony's new technology, not knowing how much effort Tony had put into it.
One possible plot reason could be ideological differences. Tony Stark is often portrayed as a tech - savvy capitalist, while Steve Rogers has more traditional values. Their views on how to protect the world, like Tony's preference for high - tech solutions and Steve's leaning towards more human - centered approaches, might drive them apart to the point of divorce in the fanfiction.
The plot could start with Steve realizing that his bond with Bucky is stronger than his relationship with Tony. Maybe there have been some misunderstandings or conflicts between Steve and Tony that make Steve reevaluate his feelings. Then, Steve decides to break things off with Tony in a rather dramatic way. After that, it could explore how Tony reacts to this rejection, and how Bucky fits into the new dynamic between Steve and the rest of the Avengers.
One reason could be jealousy. Maybe Tony has been spending more time with one of them, and the other feels left out and jealous. For example, if Tony has been helping Steve with some high - tech projects and Bucky feels ignored, it could lead to a fight. Another reason might be a misunderstanding. They could misinterpret Tony's actions towards each of them. Say, Tony gives Steve a special gift, and Bucky thinks it means something more than just friendship, leading to a fight.
One reason could be that James finally realizes the extent of his bullying. In the original story, James often harassed Snape. In fanfiction, he might come to understand how much pain he caused Snape and feel genuine remorse. Another reason could be that he discovers new information about Snape that makes him see Snape in a different light. For example, he might find out about Snape's love for Lily and how his actions towards Snape affected Lily as well.
One possible reason could be differences in their superhero duties. Maybe their approaches to saving the world clashed so much that it put a strain on their relationship. For example, Tony might be more into high - tech solutions while Steve prefers a more traditional, hands - on approach.
Maybe Steve misses Howard. Howard was his friend from the past, and he sees some similarities in Tony that remind him of Howard. It could also be that Steve thinks Tony has the potential to be as great as Howard was in certain aspects like leadership or scientific genius.
One possible reason could be Steve's strong sense of loyalty to Bucky. Maybe he feels that he owes Bucky so much after all they've been through. He might be so focused on helping Bucky or being there for him that he unconsciously ignores Tony.
Tony might be initially skeptical. He's been through a lot and has trust issues sometimes. So, he might not immediately accept Rhodey's apology. For example, he could give Rhodey a cold look and say something like 'We'll see if you really mean it.'
One reason could be to explore the extreme consequences of their ideological differences. In the official story, they had disputes over things like the Sokovia Accords. In fanfiction, this could be pushed to the limit, leading to Tony taking Steve's life.