Rather than running around a school grounds where there were students, potentially biting and turning them? Yes, Lupin. I outed you.
Did Potter conveniently leave out that it was your own fault that you were in a place to be a danger to anyone in the first place? Like presumably this army of werewolves is I kept my mouth shut for an entire year - so long as you were responsible taking the potion I was willing to abide by Dumbledore's crazy notion. You proved irresponsible - unsurprisingly - and I would have been irresponsible to not say something at that point.