Even if he still desired to do good, his anger had corrupted him to the point of no return. And this anger was amplified even further once he believed he caused Padme's death, as now he had nothing but a deep hatred for himself and everything around him.
His wife is still dead and he has done nothing to pay for his crime. Anakin does not have even the slightest bit of remorse. By the end, he feels nothing but anger. Although he feels regret for killing Padme, he still helps the evil Emperor.
Anakin's Force Choke begins the series of injuries that ultimately leads to Padme's death, and convinces Obi-Wan to fight him. Despite this, when Anakin learns of Padme's death, his immediate reaction of grief and regret shatters everything in the lab with a powerful force shockwave.
Before Padmé's death, she still believed there was still good left in Anakin, and that one day he could be redeemed. During Anakin's time as the Emperor's enforcer, he continued to suffer from grief over Padmé's death, and guilt over his supposed hand in it.
The canonical comic Star Wars: Darth Vader #7 confirms the younglings' deaths caused Anakin grief, self-loathing, hatred and pain, fueling his descent even further into the dark side.
What If Anakin Skywalker Never Turned, But Padme Died
Why did Anakin cry in Revenge of the Sith?
“The tear [on Anakin's face] says that he knows what he's done, but he has now committed himself to a path that he may not agree with… but he is going to go on anyway. It's the one moment that says he's self-aware that he's rationalizing all his behavior.
David Porter provides some great philosophical context to why Obi-Wan would not regret leaving Anakin alive, as it was obviously “the will of the Force” that Obi-Wan be unable to finish him off, and “the will of the Force” that Anakin live on to kill Sidious himself in the future.
Paul Duncan: It's implied that she lost heart. George Lucas: Yes. Her soul has been crushed. The thing that breaks Padme's heart in the end is that Anakin says to her: "Come and join me.
Being the low-wisdom guy that he was, he acted on his hatred immediately as Palapine encouraged him to do. He couldn't force-choke Obi-Wan (the one he really wanted to do it to), so he did it to Padme (the one he could do it to). Anakin believed Padme brought Obi Wan to kill him, and reacted instinctively.
What he did not see, at the time at least, was that Padmé used her last breaths to tell Obi-Wan that she was certain that in regards to her husband, "there's still good in him." Now, those words are set to be revealed to someone other than Darth Vader himself.
Before he could enter, however, Vader was stopped by Sabé, Eirtaé, Rabé, Saché, and Dormé, former handmaidens of Amidala, who refused to let him enter into the grave so he would not desecrate it. However, Vader would not be denied. As he entered the tomb, he became flooded with memories of Amidala.
Staying within the boundaries of the Star Wars canon, Vader believed that he himself was the one that killed Padme, which is why he didn't kill his master. There are many reasons why Vader didn't join the Light Side with Luke after Padme's death.
The whole reason for him turning to the dark side was to save Padme. So why didn't Vader almost immediately turn on Palpatine or just rejoin the light side after her death and the apparent death of his children? He had nothing to lose at this point and no reason to stay with the dark side.
Padme Amidala's secret marriage with Anakin Skywalker was one of the biggest reasons he eventually turned to the dark side. His emotions and love for her often clouded his judgment, and sometimes led him to be violent.
Palpatine tells Darth Vader that in his anger he killed her, placing the blame for Padmé's death on Vader. Vader denies it, saying he sensed Padmé was still alive, which the audience knows she was as Obi-Wan escaped on the ship with her.
Padmé was given a public funeral, attended by thousands. Her body was made to appear still pregnant to protect her children from their father. While Padmé died in childbirth at the age of 27, Anakin would live on as Vader until his redemption and death when he was 45 years old.
This fell in line with various fan theories and non-canon novelizations that suggested Obi-Wan and Padmé had an affair sometime during the Clone Wars. In the Star Wars prequel movies, Obi-Wan often has a duty to protect Padmé, but there was never any sense of romantic feelings.
Though Anakin's affection for Padmé was always sullied by darkness, in the end, it led to one of the truest forms of love that Anakin had ever known and Star Wars has ever seen — that between a father and a son.
This could be interpreted as Obi-Wan showing either pity or mercy for his old friend. Despite everything they have been through, the Obi-Wan Kenobi show has firmly established that the Jedi still deeply cares for his former Padawan and remembers him as the great ally he's had for many years.
After striking down his old master at the start of the original trilogy, it's fitting that Anakin Skywalker sacrificed himself at the end. Darth Vader was a terrifying villain throughout the OT, fighting his own son until the very end, which made it incredibly shocking when he threw the Emperor to his apparent death.
The novel also states that Obi-Wan chose to leave Anakin's fate up to the Force, which is a lazy excuse to remove blame from himself. Obi-Wan's actions, cleaving up Anakin's body, sealed his fate and he knew it. Obi-Wan's choice to leave Anakin was just the last way that Obi-Wan failed him as a Jedi Master.
