4. Gabby Dawson and Peter Mills
Gabriela Dawson (Monica Raymund) is best remembered for her marriage to Matt Casey (Jesse Spencer), and understandably so, but there was a brief period in season 1 in which Dawson was romantically involved with Peter Mills (Charlie Barnett) instead.
Dawson and Mills weren't a bad match on paper, as the two shared a love for cooking, but things were never going to last. Dawson was struggling with her romantic feelings for Casey, and Mills was able to sense it, leading to trust issues.
Not a baffling combination so much as one that's been lost to time.