Complex sentence: Lestat took her to his tower where they lived for several months in happiness until Lestat destroyed the Satanic cult headed by Armand, found a theatre and made Nicholas into a vampire.
Split into simpler sentences: Lestat took her to his tower where they lived happily for months. Things changed, however, when Lestat destroyed the Satanic cult headed by Armand, found a theatre and made Nicholas into a vampire.