Caitlin Snow / Killer Frost

Adaptations
Arrowverse  Hunter Zolomon  - When a man claiming to be Jay Garrick, The Flash from Earth-Two appeared in Central City to help Barry Allen defeat the villain Zoom, he and Caitlin developed romantic feelings for one another. It was later revealed that this was actually Zoom himself in disguise. He still loved Caitlin, however, and tried to get her to join his side, to no avail, before he was defeated.
 * 1)  Ronnie Raymond / Firestorm  - Ronnie and Caitlin were co-workers at STAR Labs, developing the particle accelerator. Ronnie's lighthearted nature complimented Caitlin's serious demeanor and the two fell in love. They were engaged to be married when Ronnie was apparently killed in the particle acceleartor explosion. Some time later, after Caitling had become a part of Team Flash, it was revealed that Ronnie was actually alive, wandering around homeless without memory, but with superpowers. Caitlin helped revive him, and he became the superhero Firestorm. He departed for a time to travel as Firestorm, but later returned, and the two were married. Shorly afterwards, however, when a black hole formed over Central City, Ronnie was killed by being sucked in while trying to close it. (it's possible that this romance was inspired by the storyline in Crisis on Infinite Earths where Killer Frost, Firestorm's enemy, becomes enamored by him due to a spell).

2.  Julian Albert  was Barry's associate forensic scientist at Central City PD. Although often at odds with Barry, he eventually learned his secret and became a member of Team Flash. Becoming infatuated with Caitlin, Julian attempted to woo her, but Caitlin was reluctant due to her troubled romantic past. She eventually agreed to go on a date with him. The two went on multiple dates, but eventually, troubled by her new powers that turned her into the more wicked Killer Frost, she left the group. Julian begged her to stay, telling her that he loved her, but she left anyway. When she returned to the group that fall, Julian was nowhere to be seen, and not a word of him has been mentioned on the show since.

Caitlin has also shown signs of being attracted to Barry Allen / The Flash. When an imposter inhabited Barry's body and came on to Caitlin, kissing her, Caitlin returned the kiss. Later on, having turned into the villainous Killer Forst, she chose to freeze Barry not by simply touching him, but by planting a big kiss on him. Either way, Barry is now married to Iris, so this seems like a dead issue.