[He looks a bit tentative himself- from his limited experience, he knows that girls can get upset over the strangest things. And when they get upset, it's better to not be around.]

Look, this is only my conjecture based on what you've told me- I'm sure there's more to this story. But you said you can use your magecraft to see even the past that someone has forgotten. If you and your sister were together for those ten years, haven't you searched her for some of those memories?