Do you know of any fics that center Stony, but the feelings are either unrequited, or one party can’t/won’t act on them? Almost everything I’ve found is either a twist happy ending (I think you’ve covered that from a few angles), it makes one of them the emotional villain, or it heavily involves another ship, which isn’t my thing (canon relationships that are only referenced/implied would be fine). Basically, I’m looking for stories that are okay with letting the sadness breathe.

That’s an interesting ask, but here are some suggestions for you with bittersweet endings that you might like.

THE BEST ENDING IS COMMENTS AND KUDOS FOR YOUR AUTHORS!

voglio sentirti by lackluster_lexicon:
Steve returns to Stark Tower ten months after leaving Tony in Siberia.

All That’s Left by @winterstar95:
In the midst of the civil war, Steve meets Tony at an abandoned hotel.

la douler exquise by starxreactor: “I…” Steve starts. He clears his throat. “My chest hurts. A lot. And I feel like I can’t breathe?”Tony lets out a whistling breath. He’d known Steve would have to deal
with that, but he still doesn’t like it, not just because Steve is
uncomfortable but because he doesn’t want to deal with the pity that’ll
come with it once this whole thing is over – because it will end,
there’s no way he’ll let either of them be trapped in these foreign
bodies forever.He breathes in, testing his new body. The air rushes into his lungs,
and he’s expecting the pain to blossom in his chest, choking him,
cutting it open with its thorns and letting the agonizing petals spill
out – but there’s nothing. A blank canvas, waiting for the flowers to
spatter against its surface and paint it in the colors of hurt.In a way, though, he’d almost welcome the blooming ache, prefer it to
the heavy knot of guilt sitting in his stomach, settling like a stone
in water. What right does he have to steal Steve’s body, live in it,
take care of it, use every single one of its privileges, while Steve has
to deal with Tony’s old, beaten, broken up carcass?-The manifestation of Tony’s love is slowly killing him. Steve finds out.

We’ll Always Have Paris by @missbeckywrites:
Steve wants Tony to punch his V-card, but not for the reason Tony is hoping for.

Never in Time for a Dance by @navaanwrites:
Steve learns of it on from the news.

back when the end began, we stood together for the last time by @navaanwrites:
They meet back at the beginning, and Steve knows there’s only the end to look forward to.

Minutes to Midnight by Woad:
The Illuminati wipe Tony’s memories instead of Steve’s.

Thin Line by JentheSweetie:
“I want to see him.”

Scraping Up the Pieces by @robintcj: A few years after CA:CW, things are almost back to normal. Team Cap
is back stateside, they’ve rejoined the Avengers, and they’re all
working with one another – even if it’s sometimes not all that
comfortably. Steve and Tony aren’t back together, but at least they can
be in the same room at the same time without it ending in a fight. Most
days.A rough mission puts Steve in a bad place, and Tony – who’s
in a bad place of his own – goes to check on him. Steve needs to feel
something that isn’t pain, and Tony needs to give him that.

Lost Chances by @laireshi: “Did I hurt you?” Steve asks.“No,” Tony says.But Steve already knows what Tony lying to his face looks like.

Downwards, Ever Faster by @laireshi:
“I love you, Tony,” Steve says, and Tony believes him.
Tony never thought he could be so happy. Maybe after New York and
Sokovia his luck has finally turned. He looks forward to the
future–with Steve at his side. It’s perfect.That is, until Lagos
happens, and the Sokovian Accords are thrown between Steve and Tony.
Good thing Tony knows that they can get through anything together. Can’t
they?

The Greater Good by @awesomeavocadolove:
After days of bitter arguing, Steve visits Tony’s workshop with a peace offering.

This is Not a Love Story by CMRandles:
Because they cannot fuck, they fight.

No Second Chances by Stark_Revolution:
Prior to the Time Heist, Tony Stark records a second, private video intended solely for Steve Rogers.

Sea of Petals by @cptxrogers:
Hanahaki Disease is an illness borne of one-sided love, causing
flowers form and grow in the lungs of the unrequited, the petals coughed
up with increasing frequency. If the love is not returned, the flowers
filling the patient’s chest will eventually prove fatal.
During Hickmanvengers, Steve and Tony are both keeping secrets from each other.

Another Night in Madripoor by Captain_Al:It’s been five years since Tony Stark left New York to
start Stark Resilient and didn’t look back. When he and Steve Rogers
meet by chance on a trip to Madripoor, Steve proposes something that he
thinks could resolve their lingering feelings for one another. Alternating POV, AU from Siege. Basically what-if they never made up during Avengers Prime.

Chasing a Ghost (Sound of Footsteps Remix) by @captainneverever:
Tony finds traces of his possible soulmate in archival records.

only one life to lose by @msermesth: “I’m from a future.” Nathan’s smile falters but his gaze doesn’t change. “And hopefully not the one you’ll see.”For Tony, that is all sorts of unsettling. “Why are you here?”Nathan
pulls something from his pocket that could be a watch but clearly
isn’t. “Because I need an assist, and you’re the smartest man I know.”

Public Enemies (the Secret Lovers Remix) by @msermesth: “They have a video of Steve and I. Together.”
Tony pauses and hopes Maria won’t make him explain further. A quick
check confirms that it’s already on YouTube. In one-point-five minutes,
it’s going to be trending on twitter.“Why didn’t you tell me?” Maria stands, defiance written in her eyes, and Tony knows she already has a plan.Tony mirrors her posture. “Because you don’t get to know everything about me.” You don’t get to taint this for me, he thinks.   I’ve done a great job tainting it all by myself.

All Time Low by @sineala:
Tony’s lost his company to Obadiah Stane. He’s lost it all: his money,
his friends, his Avengers team… and his sobriety. Drunk, homeless,
Tony is living on the streets, and when he runs out of liquor money, he
sells the only thing he has left: his body. And one day, he has the
exact wrong customer.

A Real Boy by @sineala:
When Steve shows up for the Avengers’ team meeting, he quickly discovers
that the version of Tony in attendance this week is the artificial
intelligence. But Tony is still Tony, the man Steve has loved for years,
and him being a hologram doesn’t stop the two of them from falling for
each other. They just have a few kinks to work out.

Sucker Punch by @sineala:
Steve never quite warms to Tony Stark, Avengers benefactor. The Molecule
Man never strips Iron Man out of his armor. Life goes on for the
Avengers, but as disagreements split the team – and Shellhead and
Winghead – again and again, Steve wonders why Iron Man always picks
Tony over him. And when Steve finds out, it happens in the worst way
possible.

Some Great Reward by @kiyaar:
After the events of Captain America: Civil War, Tony and Steve come to an agreement. It doesn’t involve affection.

Take My Body Home by @kiyaar: After the events of Superior Iron Man, Tony sells Extremis to the
highest bidder and finds himself living as an expatriate in Russia.Steve’s never been good at letting go.

Plunge by @kiyaar:
How the Illuminati ruined everything and no one was able to pick up the pieces.

Make Believe by CAPSING:
Tony deals with his problems by making them go away, as he sinks into the realities he creates using B.A.R.F.

Lie on the Floor Without Holding On by @festiveferret:
Tony flails against the shifting of gravity, trying to figure out why “up” suddenly isn’t where it’s supposed to be anymore.

Multitude of One by @nostalgicatsea:
“So was I,” his soulmate would tell him one day, and what it would mean was that they loved him.

the calculation by tonystarxk (romanoff): One year post-Civil War, and the team are back together.At least they’re back living together. As in cohabiting the same space. ‘Back together’ is probably too optimistic.(thanks to @the-ironphoenix for the suggestion)

Prima Nocta by sabrecmc:
This was a Thank You Fic request for Anon, who wanted to incorporate
Tony’s reference in AoU to prima nocta and bottom!Steve.  Please note
that, despite the premise, there is no non-con between Steve and Tony.
Took me a while to think of how to do that, but here we are.  There is
definitely gratuitous fetishization of Steve’s virginity, however.  If
that bothers you.  If not, pull up a chair and enjoy.

In Dreams by sabrecmc:Steve enters Tony’s dreamscape to save him and finds a lot more than he ever expected. From
the kink meme: Tony and Steve ending up in some dreamscape where they
can see each other’s fantasies as a distraction technique from some
villain (I don’t care which). Steve opens the door to Tony’s dream and
sees 3 Steves (I’m not picky which) topping Tony. Up to author how Steve
reacts and if this is a established relationship or not.