Complex sentence: Blair finds herself in a dilemma as her feelings for Chuck have resurfaced, arriving at the party to inform Louis of her decision but Chuck interrupts her, informing him that he has their blessing.
Split into simpler sentences: Blair finds herself in a dilemma as her feelings for Chuck have resurfaced, arriving at the party to inform Louis of her decision. Before she tells Louis, Chuck interrupts her, informing him that he has their blessing.