Complex sentence: While Grubitz sees the situation as an opportunity for career advancement, Wiesler is horrified by the abuse of power, and through his surveillance, recognizes that Dreyman and Sieland are deeply in love.
Split into simpler sentences: While Grubitz sees this as an opportunity for career advancement, Wiesler is horrified by the abuse of power. Through his surveillance, he knows Dreyman and Sieland are deeply in love.