Complex sentence: Then she tried to have a convent ceremony with Alexander's best friend, Sebastien, but Raven found out that they were really on sacred ground and tried to stop it only to be dragged aside by Jagger at the last second.
Split into simpler sentences: Then she tried to have a convent ceremony with Alexander's best friend, Sebastion, but Raven found out that they were really on sacred ground and tried stopped it. Only to be dragged aside by Jagger at the last second.