5. Gianna Mackey and Blake Gallo
Blake Gallo (Alberto Rosende) may have had his most meaningful connection with Violet Mikami (Hanako Greensmith), but the firefighter did have romantic chemistry with paramedic Gianna Mackey (Adriyan Rae) in season 9.
It's worth noting that Gallo and Mackey never went out on an official date, but the groundwork was being laid for what looked to be something notable before the character of Mackey was written off the show.
Because of Mackey's premature exit, and Joe Cruz (Joe Minoso) warning Gallo from romancing the paramedic, this could-have-been romance never got the shine it deserved.