What TV series suffered by introducing an unnecessary romance between characters? And in the reverse, are there any TV series that suffered by NOT introducing a romance between two characters?

Garak and Bashir

In the first season of Brooklyn 99, there is this weird plot line where Charles develops a crush on Rosa and she keeps telling him to back off. Likely done at the time to foil Peralta and Santiago's immature, pig tail pulling romantic arc, but anyone whose watched more than a season knows those two characters are totally wrong for each other.

Its a little funny because it doesn't come off as early writing weirdness. Charles was going through a really rough divorce at the time, and Rosa, while gruff, does deeply care about her friends (and him), and didnt want to slap him down. He later apologizes, and dates a few other women before settling in with a new LTR.

The entire Arrowverse.

supernatural, apparently they introduced a gay/homoerotic relationship between the characthers, after season 5, it was pure fanfiction. which grew into a obssession by fans to the point they became extremely creepy and parasocial. the show was meant to end by season 5 but kripke had left by that time, and the 2 others decided to do it.

romance just puts the show into the "drama" category when it shouldnt be and it ruins the show. like a sci-fi shouldnt have ovvereaching romantic drama that is not part of the sci-fi plots. SGU to give an example

Joey/Rachel on Friends.

Community with Troy and Britta and Annie and Jeff. After Dan Harmon was fired and replaced by David Guarascio and Moses Port, they decided to ruin the show in season 4 with awful writing and character choices (probably at the behest of the network). This included a sudden nonsensical Britta and Troy relationship and weird romantic stuff with Annie and Jeff in one episode, which may have been the worst Community episode imo. The whole of season 4 mostly sucked with just a couple of bright spots. Fortunately Harmon came back on board, righted the ship and wrote 2 more enjoyable seasons.

The show had lost its magic long before, but the Walking Dead matching up Rick and Michonne. Having read all the comics, they are so wrong for eachother. Great friends, but not relationship level. The big mistake the show made was casting a terrible actress for Andrea so they had to kill her off and thus took away Ricks love interest from the comics.

It really was one in a long list of bad decisions that destroyed an excellent show.

I never finished the show, but the first seasons of The X-Files was really good about keeping Mulder and Skully from getting too romantic. Made it easier to focus on the monster of the week.

Maybe unpopular opinion. But I think Buffy was ruined by all the love triangles and moping and whining going on in later seasons

[off topic?]

I thought that 'Cloak and Dagger' was one of the better Marvel shows. One thing I liked was that there was never a hint of romance between the leads; they were good friends who weren't mooning over each other. Turns out the writers were saving the romance for the next season, which never got made.

The Night Agent. It was a proper good show until out of nowhere they started eating each other's face. Completely unnecessary and it made the second season way more predictable.

Studio 60 on the Sunset Strip by Aaron Sorkin. About halfway through the first season, the character Danny (Bradley Whitford) pursues Jordan (Amanda Peet). It gets creepy cuz she initially denied his advances, yet he denied her denial.

The story arc happens around the time Aaron Sorkin was writing the teleplays based on other writers' story input. IMHO, it ruined the show.

One of the later seasons of Earth Final Conflict. They built up the female support role to be this tough brilliant independent woman who didn’t need no man. Then when the male lead left the show and she took the lead roll they immediately had her fall into a romance with some no name character that wrecked her confidence.

On the reverse, Sliders, the male lead and female support had this will they won’t they for a bit, but then in an awkward scene later between the two support roles she relates that off camera they had “the talk” and said they weren’t an item with no real feeling about it.