Complex sentence: She was once best friends with Yuu's mother, but their friendship eventually started to fall apart when Yuu's grandmother died; after Haruka and Miyuki visit the past, Asuka and Miyuki re-affirm their friendship.
Split into simpler sentences: She was once best friends with Yuu's mother, but their friendship eventually started to fall apart when Yuu's grandmother died. After Haruka and Miyuki visit the past, Asuka and Miyuki re-affirm their friendship.