His relationship with Obi - Wan would have been much more positive. There would be no betrayal, and they could have continued to be master and apprentice, or perhaps even equals as they both grew in the Force. With the Jedi Order intact, they could have worked together on many important missions. Anakin would also have a different relationship with Yoda. He would be seen as a more stable and reliable Jedi, and Yoda might have given him more responsibilities within the Order.
Anakin's relationship with Padmé would have flourished. They could have been open about their relationship without the fear of Anakin's fall to the dark side. They might have been a power couple in the galaxy, using their influence for good. And his relationship with his children, Luke and Leia, would have been that of a present and loving father. He could have trained them in the ways of the Force from a young age, and they would have had a much different upbringing compared to the original story.
If Anakin never turned, Luke and Leia would have grown up with their father. The Skywalker family would be united, and they could all be trained as Jedi. This would make them a powerful force for good in the galaxy. Also, the Sith would likely have a harder time achieving their goals without Anakin as Darth Vader.
Well, at first, they might seem closer as they are now both part of the same 'dark' world. But soon, the dark side's influence of greed and power - hunger would start to drive a wedge between them. Anakin, with his already tumultuous relationship with power, might try to dominate Ahsoka. Ahsoka, having been dragged into the dark side against her will perhaps, would resent Anakin for it. Their relationship would be a volatile mix of shared darkness and individual power struggles.
If Anakin hadn't turned, the Sith's plans might have been foiled. The balance of power would have remained with the Jedi, and galactic conflicts could have been avoided or resolved differently.
Well, the galaxy would have been a much more peaceful place. The Jedi Order might have remained strong, and there would likely have been no rise of the Empire.
His relationship with Alfred would be severely strained. Alfred has always been Batman's moral compass and a source of support. If Batman joined the Dark Side, Alfred would be heartbroken and would try his best to bring Batman back to the light. There would likely be many arguments between them as Alfred tries to remind Batman of his true values.
If Anakin never turned to the dark side in the fanfic, the galaxy would be a very different place. The Clone Wars might have ended sooner, as Anakin's strategic brilliance could have been fully utilized for the good of the Republic. He would still be a symbol of hope for the Jedi and the people of the galaxy. His friendship with Obi - Wan would have remained strong, and they could have achieved great things together as a team of powerful Jedi.
If Anakin never turned to the dark side in comics, the Jedi Order could have remained strong and continued to maintain balance. Maybe he would have become a great Jedi Master and trained many new padawans.
His relationship with himself would also change drastically. He would have to grapple with his new identity as a dark side user. There would be inner turmoil as he might still have some remnants of his former self. He could struggle with the moral implications of his actions and the new powers he has. This internal conflict could also affect how he interacts with others, making him more unpredictable and volatile in his relationships.
One way to write it is to focus on Anakin's positive relationships. For example, if his bond with Obi - Wan was strengthened even more, it could prevent his fall. The fanfic could show more of their training sessions together, with Obi - Wan guiding Anakin through his inner turmoil in a more effective way.
With his mentor or teacher figure, the dynamic would shift. Instead of being the student who is learning, Robin as a kid might be more in need of basic life lessons. His friends who were used to his equal partnership would now have to be more patient and understanding. They might find his child - like innocence endearing but also frustrating at times. And his relationship with any rivals could become more complex as they might not know how to deal with a kid version of him.