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.