One problem I see on occasion from works including unrequited love is a failure to really keep the plot from melting together, so a relationship that's meant to to come about later and is currently unrequited (or may not even be intended to reach fruition in any meaningful way) is still treated as being canon for all intents and purposes. Sometimes it's in the form of the story treating it as a betrayal if one of the non-partners hangs out with someone else, other times it's just a general way of portraying the relationship that makes it feel like they're supposed to be a couple even if they're not actually one. It's one thing if the characters feel a certain way, and relationships come in many forms, but it can be a real issue when a relationship comes across as unhealthy and the author seems to be tipping the scales.

Of note, the core weirdness isn't necessarily romance related or even intrinsically bad. The fact that some beats are effectively foregone conclusions is usually a fairly banal writing trope, Plot Armor and the Unspoken Plan Guarantee are tropes that have basically become part of the common lexicon by now. It's when it starts to monkey up the timeline of the story that it becomes a problem, when the story starts acting like characters already know things or have already done things that haven't happened yet. When romance is involved, it also carries some rather Unfortunate Implications by reinforcing a cultural problem of people feeling like they have some sort of claim on others because they're attracted to them, even if the other person never agreed to any sort of relationship or even fully rejected them...

All that's certainly not to say unrequited love is a bad plot beat, but that this is one trap to watch out for when trying to write it, especially given how heated people can get about romance.

Unrequited love is one of the more difficult romance tropes to handle. On one hand you have a relationship between two characters where feelings are very one-sided and seemingly go nowhere. On the other you have a chance to show off a reason why there is this rebuff. Like in real life, not everyone in a story gets a happy ending nor does the hero always get the girl or guy as the case may be. One of the any ways I've seen this is by having the character who is on the receiving end of the affection be some sort of cosmic plaything where they are doomed to some inescapable destiny of doom. While this certainly explains it, it's almost like you avoid the issue by making it a complete non-start.

There are countless ways that this can be done without detracting too much and without having to resolve the relationship by having the object of affection slowly come around. Take this for example. Five adventurers set out on a trip. Kate is over heels for Clark. Clark is pining over Claudia. Claudia however wants Kate. Violet and Pine are twins and can't pick who out of the other three to go after. Now, all of them are aware of the attractions and Claudia as our example only has eyes for Kate. The other three might as well not exist for her as romance options. No matter how often Violet or Pine say something to her, she'll be gentle and say no to it. You can keep this dynamic right on through even if Claudia doesn't get Kate in the end. The one sided nature of this can actually spur your character to act rashly in front of the object of affection ad maybe even sacrifice themselves to save them.

This particular relationship is difficult because we want a relationship to be a two way street. We love seeing characters slowly fall for each other. So when we run into this type of relationship where the love is heavily one-sided and not returned, we wonder why and maybe even write fanfiction about these characters where they don't have these hang-ups.

The thing to remember is this. Real life love goes unrequited all the time. There's no rhyme or reason as to the fine details of why or how as there are many explanations. Having a character experience this may allow you to bring someone into their life that's willing to return their affection. Then you can pull them slowly together and go from there. Equally reasonable is to just let it happen and stay that way. After all, the hero doesn't always have to get the girl at the end.

Two authors come to mind when I think about unrequited love in literature. One, of course, is Hemingway. The other is William S. Maugham, especially in Of Human Bondage. Unrequited love is a major element of the protagonist's character development.

It's readily apparent that both of these guys experienced their share of unrequited love in life. I think - without that personal experience - writing about anything related to love is less poignant and not as believable.

That said, if you've never experienced unrequited love, it's worth missing out on. It's not a requirement for eventually finding a person who loves you back.

I think unrequited love is denoted through writing out the feelings of most usually longing, sometimes abandonment, and pain. There can also be the feeling of loss. The best piece of advice that I've received and that I would like to pass on is: go through it. But in all honesty, that piece of advice was given to me for all writing. After all, writing based on experience is much more straightforward.

Emotions are difficult to portray through words a lot of times, and that is because emotions rarely make a lot of sense. There is no logic to be found in them, especially in love. I personally think that the most reliable way to truly understand what love is like, or what unrequited love feels like, is to go through it. Not that I would wish for someone to go through all the pain that a love unrequited brings.

Further, I think there's this idea that some people have that love is all flowery, and thus should be portrayed as such. I think that to properly tell any tale revolving around love, the thorns should be shown to the reader as well, and not just the rose petals on top.

Motivation for staying in a situation of unrequited love is also an important factor when writing. Are they emotionally immature and don't realize their feelings, leading to anger/jealousy/a sense of ownership over another? Do they feel as though their feelings are wrong and are fighting themselves using said feelings or societal expectations? Do they value their friendship and occasionally have bursts of romantic thoughts that ebb and flow throughout the decades?

Where they place their feelings as rank of importance in their life will guide a lot of action, and of course, your writing.