"But you changed," Obi-Wan answers. He pauses, feeling Ben's presence in the Force. "She changed you?"

It isn't entirely a question, but he prefers not to make any assumptions without confirmation, even when he could reach out deeper into the Force and probably develop a bigger and clearer picture. This is Ben's story to tell if he wants, if he's willing to share. There's no reason for Obi-Wan to try to unlock more than he's allowed to know.