You've joined the X-Men probably around 5 years ago at max. You've done your research on most, if not all, the X-Men members there. You know their powers, weaknesses, etc, etc.

Most of them knew you would possibly be a liability if you turned on them but Charles had faith in you, same with Colossus.

It was all fine and dandy on a mission with some of the members until you felt off, feral even. Soon you weren't in control of your own body for some reason and started to run after Nightcrawler.