1. Sylvie Brett and Antonio Dawson
This one is tricky. Some fans really liked the pairing of Brett and Chicago PD's Antonio Dawson (Jon Seda). They brought out different sides of each other's personalities, and they had some electric chemistry whenever they were together. They were, pretty plainly, though, a bad fit.
Dawson was not interested in settling down with Brett, and there were long stretches of their romance where it felt as though Brett was way more invested. Case in point: the season 6 episode in which Dawson tells Brett that he's seeing someone, right before Brett planned to propose they get back together. Not ideal.