did Anakin only become a Sith when he protected the Jedi code

Anakin became a sith because his killing of mace windue was the point of no return for him .

 

Well killing the emperor would have been shown as simple self-defense but Anakin was extremely in the moment...you are right that what he did officially was still defending the jedi code but I also doubt harming another jedi is a part of that code too..

 

I don't think it was the fact that he disarmed Mace that cemented his fall, but the fact that he did nothing to prevent Palpatine from murdering him. If he still followed the Jedi code, he would have protected Mace Windu as well. So in reality, Anakin Skywalker was half-right.

 

I'd agree to a point but, as @Alex Sebire said, it's still called 2nd degree murder or something like that if he simply stands by to allow Palpatine to kill him him...if anything he should have cut off Sidious's hands too
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He beheaded Dooku in a fight TO THE DEATH...his killing of the tusken raiders was him losing his mind...I mean, would YOU sit still and move on if a group of people killed your mom and you had the power to stop them? i know it's a dark thought but that's similar to what's in his head when it happens...Lucas himself said that the scene is meant to show his start towards his fall because he is incapable of holding back his emotions and keeping them in check...Anakin was never particularly close with Mace even saying that he doesnt trust anakin until his accusations are proven correct but it's his duty as a jedi to protect others; What he was thinking in that moment in letting Windu die was that "What if The Chancellor Is right that he can save Padme?" If he were to interfere then maybe Padme will die (which she did regardless)
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Maybe it could have been better with the fight alsting longer and mace begging anakin to fight alongside him, which he does initially, but then mace is injured and he force-lightnings Anakin instead for "betraying" his trust until Windu comes back to save the day and Anakin is too weak to stop Palpatine from killing him but then he apologizes to his new master and vows his allegiance as a sith apprentice.

 

I thought I felt the ambiguity a bit...it's very subtle but it's there, it's hard to tell because it's mainly an internal conflict..

 

Or maybe if Palpatine thinks Mace is dead and Anakin says, "what Have I DONE?!" and pledges himself as a new sith apprentice and that's when Windu gets up in horror and then tries to also arrest anakin so anakin kills him
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No. Anakin became a Sith when he vowed to serve Sidious and commenced upon attacking the Jedi Temple and killing the Separatist leaders.

 

I don't think Anakin became a Sith until he said, "I pledge myself to your teachings." When he cut off Windu's hand, he didn't intend to become a Sith, and becoming a Sith requires intent.

 

There are really two different questions here. One is, "When does Anakin formally become a Sith?" which is pretty obvious, as noted above. However, there is a second question, which is "When is Anakin's fate sealed?" A major theme of Star Wars is a balance between free will and destiny, so you could potentially make the argument for anything from "Anakin was doomed from birth" to "Anakin had free will and could've turned back until the last possible moment".

According to Yoda, "Once you start down the dark path, forever will it dominate your destiny, consume you it will," so it is possible that Anakin's fate is sealed as soon as he attacks the Tusken Raiders. However, even Yoda's statement is potentially ambiguous, because he could be speaking in terms of destiny ("Once you start down the dark path, it is literally impossible to turn back") or in terms of psychology ("Once you start down the dark path, no one ever chooses to turn back").

Yoda is very wise, but he is neither omniscient nor infallible, so there is also the possibility that Yoda was wrong. Depending on your point of view, Anakin's redemption may have disproven this statement. Also, "oracle"-type characters are sometimes known to tell people what they need to hear, rather than telling the literal truth.

In short, I believe Anakin's point of no return is intentionally left open to interpretation. I think it conveys messages both about making decisions and about fulfilling your destiny.

 

No one becomes a Sith instantly. Same as how no one becomes a Jedi instantly. It takes a lot of time. Palpatine has been training Anakin to become a Sith ever since he arrived at the Jedi Temple. Read the Anakin and Obi-Wan comic. Palpatine has been manipulating Anakin since the very beginning. At what point did Anakin become an official "Sith"? When he pledged himself as Palpatine's apprentice. "Always two there are". Maul isn't even a Sith anymore because he is no longer an official "Sith" anymore after Palpatine chose another apprentice.