I havent really been readin, but this is how I sum it up....
Okay, Im guessin, Roxas joined the Org. sometime near the end of KH1...in an Ansem report, it said he encountered Xemnas in Twilight Town *Im guessin the real one* and Xemnas let him join because he could wield the keyblade....I guess Roxas wanted to understand why he was chosen by the keyblade,, so he left...
around the same time, Riku and Diz met in Twilight Town....If Im correct, Diz said that in order to complete Sora, he needed Roxas. When Riku went to get Roxas, he lost a fight with him, but the second time, he used the power of darkness and gained Xehanorts form...Then Riku *still in Xehanorts form* took Roxas to Twilight Town, and Diz turned him into data with a new personality and sent him to a simulated town...that why he didnt remember anythin....he was given a new personality, to keep him at bay until Sora would awaken from the pod...
is that about right???