4. Brittany Baker and Kelly Severide
Severide strikes again! The character was distraught after Shay's death, so he took a trip to Las Vegas. When he came back, he was married to a complete stranger named Brittany Baker (Serinda Swan)! Baker was a perfectly sweet person, and she got along with Severide much better than one would think given the circumstances in which they got hitched.
Still: the whole storyline reeked of a cliche TV trope. A similar plot line had been trotted out for That '70s Show years prior, and fans knew that the marriage between Severide and Baker wasn't going to last. We were right!