Mon-El and Kara - Supergirl
Mon-El was Kara's greatest love which is why she was able to remain cool when he returned from the future a married man. Kara's greatest powers as a superhero include: being sweet and helpful to her ex's new wife, Imra, being understanding enough to have a heart-to-heart with him as they did back in the day, and working alongside him for the greater good of planet Earth.
Petra and Rafael - Jane the Virgin
The former husband-and-wife duo remained friends following their split and even continued on with their hotel business. Though they gave their relationship a few tries, they eventually realized that they were better off as friends. Rafael was so understanding of Petra, he wasn't even scared away when she inseminated herself with his sperm without his consent. And when she began having feelings for a woman, he was the one who encouraged her to follow her heart.
Nic and Conrad - The Resident
Nic and Conrad weren't together for the larger part of season one, however, they remained civil and worked well together to save lives. Later, we found out the rift between them was caused by a miscarriage and Conrad's inability to express his emotions following his time in Afghanistan. They may be giving their relationship another go now, but they've already proved that regardless of what happens, they are friends first and lovers second.
Ruzek and Burgess - Chicago PD
Ruzek and Burgess' relationship was short-lived. Fans want them back together and maybe one day it will happen, but for now, they are supporting each other, dating other people and focusing on their careers. Since calling off the wedding, neither held any resentment towards the other because they weren't ready for that next step. Burgess calling it off was a chance for both of them to reassess the relationship and strengthen their foundation as friends.
Mellie and Fitz - Scandal
It takes a strong woman to stay with a man, specifically the President of the United States, when he has a mistress. It takes an even stronger woman to later befriend the mistress and work alongside her during her own monumental Presidency. In summation, Mellie was one strong woman who accepted that their love story fizzled out and their relationship entered a platonic phase. Fitz was the only one who understood the difficulties of holding the Oval office and he offered guidance and support throughout her run.
FP and Alice - Riverdale
FP and Alice weren't always on friendly terms, however, they found their way back to each other after their children Betty and Jughead began dating. FP helped Alice tear down her overprotective wall and helped her connect with her inner-Serpent again. Sure, there is still major chemistry between them, but for now, they remain friends who keep each other sane in this dark town.