Truly sorry, M.Mario, that you, and your whole community, are dealing with this. While a certain amount of survivor type guilt is unavoidable, I agree with Amos, guilt, like worry, is bootless, and I've come to feel that it is actually a negative state in that it mires us in the past, when, again as Amos says, what needs focus is the future. I hope you can take comfort in the fact that you were instrumental in getting help for your nephew.
Triggers are irrational...you're way ahead of the game if you can see them for what they are, and move on. Take care of yourself--these are trying times, and people like you, with strength and sensitivity are needed now, as always.