The Marvel Cinematic Universe of course takes its cues from the source material. A huge part of the comic book world is setting up these heroes and villains with love interests. These roles allow for an increased amount of conflict and create a more relatable narrative arc for the larger-than-life characters.
A love interest can therefore aid the story in plenty of ways, but that doesn't mean that every character in the MCU actually has one to work alongside or bounce off of. Whether they've been too busy fighting crime or have had a troubled past that they haven't quite healed from, these characters are yet to find romance on screen.
Captain America
Sam Wilson started off life as a military man, before suiting up as Falcon. As an Avenger and current Captain America on the path to drastically change the MCU, Sam has given most of his life to protecting his country. Now acting as a veteran superhero, it might finally be time for him to settle down; if he wants to, of course.
Recently fans have been particularly enthralled by the bromance between Sam and Bucky which has continued to develop. As Sam hones his craft as the new star-spangled man, he may begin learning from Steve Rogers' life and look to live a peaceful existence of his own when the time comes.
Captain Marvel
Captain Marvel spent the majority of her life surrounded by a lie, working for the Kree Empire. With very little memory of a time before her service as a soldier, Captain Marvel has really no romantic ties on Earth. It appears she also didn't form any while living on Hala.
The character, extremely powerful in all her versions, is really the last line of defense for plenty of planets across the universe. She's always needed somewhere and that leaves almost no time for romantic attachments. Carol Danvers always puts her duty first which is one of her most admirable traits.
War Machine
James Rhodes has watched on as Tony Stark has had numerous relationships (some of which haven't lasted overly long). As a man of duty himself though, there doesn't appear to be a love interest in War Machine's past or future. There could be some clues in the source material though.
Fans of the comics will know that one of War Machine's major love interests is actually Carol Danvers. The two both have a military background and share plenty of the same values. While they haven't interacted much on-screen yet, maybe there is a romance in both of their futures.
Wong
Wong is a loyal member of the masters of mysticism who protect Earth from otherworldly threats. There might even be a sworn oath that Marvel fans don't know about, but this doesn't seem like the sort of location where romances with colleagues would be allowed.
Audiences don't know much about Wong's past in the organization. Perhaps more will become clear as the MCU develops, but it may be that Wong has been learning magic for most of his life. His duty will likely get in the way of ever being able to find love. For now, fans will have to settle for his memorable bromance with Doctor Strange.
The Winter Soldier
Bucky Barnes has been seen with a few partners in the past, but none have been treated as major love interests. After seemingly dying, getting turned into a killing machine, getting over his brainwashing, and ultimately becoming an avenger, there wasn't much time for dating.
Bucky has tried to find a way back to the world of romance but has been seen on only one date. He may have some interest in Sam's sister although Wilson has made it very clear that he doesn't approve of the coupling. It's almost inevitable that Bucky will get to find the person of his dreams though.
Ayo
Ayo is one of the leading members of the Dora Milaje, the warriors who protect Wakanda from all manner of danger. Romances are not banned from the group, as Okoye is known to have a major love interest in her own right. Ayo seems more concerned with her role as a soldier for now.
The character has had an increased spotlight in recent times and is likely going to continue being one of the major Dora Milaje featured. However, her story doesn't seem to accommodate romance for now and Okoye has demonstrated that personal loyalty can severely impact a Dora Milaje's role as a fighter if their love is on the other side of their blade.
Rocket Raccoon
Rocket Raccoon has his best friend in Groot, but there has been little in the way of love interests for the character. He has got to accept himself before he can allow anyone else to love him and he seems to struggle majorly with his confidence and self-worth, something fans feel bad for when it comes to Rocket.
In the comic books, Rocket Raccoon does actually have a romance with a cybernetic Otter named Lylla. It's possible that the Marvel Cinematic Universe brings in the character to help Rocket heal himself, but for now, he finds his loneliness is comforted by his found family.
Valkyrie
It seemed for a brief moment that Valkyrie would act as a love interest for Thor, however, this very quickly passed. The Asgardian has spent many years as a hunter and has clearly spent most of them drinking and partying without forming many emotional bonds.
However, the Queen of New Asgard may be looking for a Queen to share the throne with very soon. The character could well find her own romance in the appropriately titled Love And Thunder, but being Queen will likely be a very busy job! Perhaps there's just no time for love.
Black Widow
Yelena Belova has only just been introduced to the Marvel Cinematic Universe, but already fans are taken away with her. Belova has spent most of her life brainwashed by the Black Widow program and therefore hasn't developed much of a social existence outside of this.
She's only just reunited with her family, but perhaps there will be room for some love interests in her future appearances. Natasha Romanoff briefly bonded with Bruce Banner in her own right, but there's no telling whether Yelena will have a happier ending in the world of romance.
Thanos
In the comics, Thanos famously tries to court Death. While this romance was briefly teased in the MCU, it appears his only love was for the Infinity Stones. Regardless, Thanos builds up his own family, with Nebula and Gamora as his two adopted daughters.
This abusive father certainly didn't deserve any love from his daughters though and indeed never found a love interest to perhaps share his family with. It would have been intriguing to see Thanos obsesses over Death herself, but ultimately his motivations were compelling enough.