Complex sentence: However, the main difference is that Belle quickly saw Gaston for who he is and mistrusted him, whereas Hans gained Anna's trust before betraying her and making her realize the warning Kristoff gave her about falling in love with someone she doesn't know was true.
Split into simpler sentences: However, the main difference is that Belle quickly saw Gaston for who he is and mistrusted him. Whereas, Hans gained Anna's trust before betraying her and making her realize the warning Kristoff gave her about falling in love with someone she doesn't know was true.