There are a couple of tropes that have long bothered me--not necessarily in each instance of their use, but I wish those uses were less frequent. One is the character whose unrequited love persists for decades; the character forgoes all other chances at happiness and clings to the love that can never be. Now, this story line can be done well, and it has been ... but in real life more often than not, people get over it. Even if they carry a small torch somewhere in the backs of their minds for a lost love, they still find new relationships and happiness. As my friend Kelly Fineman has pointed out, Jane Austen knew this--her Rakes who Didn't Get the Girl did not pine away for the heroines forever. Mostly, they married others and had lives of their own. I find the unrequited love especially annoying when it's a minor character who seems to exist solely for the purpose of having a futile crush on the main character (and sometimes, to cheer on the main character's successful union with the main love interest).
other pattern I dislike is the one where only the main couple in a story
gets to have a love life, and all the minor characters are window
dressing with no romances of their own. One reason I liked the TV show The Office
was that the secondary characters, like Phyllis and Erin and Angela and
Oscar, got to have their own love lives. (Although it bothered me that
Toby ended up falling into the other trope, with an endless unrequited
crush on Pam.) The rounded secondary characters in that show delighted
me, and I've always wanted to recommend it to writers for that reason
(and now the show is ending. But hey, it lives on in syndication.)
reality, we're all the stars of our own dramas, and not likely to
sacrifice our love and all our hopes and dreams to the interests of some
other "main character." In our own minds, we're the main characters.
Every side character in a story is the main character of his own life,
and his actions should happen accordingly. If he helps or hinders the
story's main character, it should be because his own interests happen to intersect (or conflict) with the main character's interests.