Complex sentence: Margaery later visits Tommen one night where he reveals his Pet Cat Ser Pounce, and for the fact that he and Joffrey didn't get along and he and Margaery bond over their mutual relief that they are free of him.
Split into simpler sentences: Margaery later visits Tommen one night where he reveals his pet cat Ser Pounce, and the fact that he and Joffrey didn't get along. This causes him and Margaery to bond over their mutual relief that they are free of him.