> What did I do?
 >>/1141/
> What could I have done?
you were a filly, Dolores. Everybody makes mistakes 
> What would I have done?
Simply be a better a pony, not like it´s too late for that.

> With so much power...
The bigger the power, the more responsibility. Sometimes it´s better to live in peace with yourself, do your thing and make your own life without stressing so much about others.
> Would I have lost myself?
It was bound to happen, considering that you were like Twilight but more anxious and desperate for friendships.
> Would I have lost everything trying to get there?
Do not think about what you could have had, think more about what you have now. 
> I silently look back in horror to what I could've have been
Everyone has those moments. At some point you will say that you were stupid and you won´t take those in depth thoughts so seriously after a certain period.
What´s more important is the lesson learned here.