Complex sentence: First, Blane suggests going to a party Steff is throwing but the party isn't exactly what Blane expected, and Andie is treated poorly by everyone, including a drunk Steff and Benny.
Split into simpler sentences: First, Blane suggests going to a party Steff is throwing. But the party isn't exactly what Blane expected, and Andie is treated poorly by everyone, including a drunk Steff and Benny.