I exited act 1 through the door. Then I realized that you can also destroy the citadel with the bomb.
So I loaded a previously saved game and made the bomb.
Well the only difference is that I exited act 1 with more experience. So does blowing up the citadel change the storyline? Because it seems that the citadel is still there in act 2 and so far the characters don't mention anything about the citadel being destroyed.
Was it supposed to be destroyed or is my game broken or something?
Nope, everything is fine - just continue. There is no cutscene about an explosion - you can't reenter. Difference => bomb exit is 22646 XP, key exit 0 XP.