At the end of 358/2 days, Xion had a talk with Namine about how she and Roxas would need to get absorbed back into Sora, and they both agreed on that Roxas wouldn't understand the whole situation and why they need to do everything they do because he doesn't feel Sora yet.
Why would they say that?
At day 321, Xion and Roxas had ice cream again at the clock tower, and Roxas asked himself how Axel could attack Xion on day 298, even calling him a jerk. But on that same day, Xion raised her keyblade against him, and yet, he doesn't seem to hold it against her. He seems to trust her a lot, so he probably would believe her if she said the truth and he would understand it if she explained it properly.
This might be my bias, but it seems incredibly unfair for Roxas that Xion is explained everything about the whole situation, while Roxas is kept out of the dark, especially since he wants his answers so much and since the decisions they make is something that will have a big impact on both Roxas and Xion, not just Xion and they all know it. While I can understand her not telling him since he trusts Axel so much and he would most likely tell Axel, who will then stop her, what Roxas said on day 321 did make it clear that he did not trust Axel as much, so she could have told him everything and convinced him not to tell Axel everything.
I don't hate Xion at all, in fact, I like her, but this is something that has been bothering me.