Hi, firstly, thank you so much for all that you do for the fandom. You are an global Stony treasure, and we are all indebted to you. Secondly, after seeing IW and being suitably traumatized, I am a little sad that we didn’t get the reunion we were all hoping for. In lieu of that, fanfiction is the way to go. Could you perhaps recommend some fics in which Tony and Steve are intensely in love with each other, to the point of bordering on obsession maybe? My heart and I would be very grateful!

Hmmm, well, there are some great fics with sort of obsessive behavior, though mind the tags. Not all of this stuff is healthy relationship territory.  I feel like these are mostly darker than what you are wanting, and some are  more one-sided, but still fit that basic idea of obsessive love. That being said, here you go:

AUTHORS ARE OBSESSED WITH YOUR COMMENTS AND KUDOS!

Obsession by coffee_and_angst24:
Tony won’t commit to Steve but he won’t let anyone else have Steve either.

kissing the bruises left behind by theappleppielifestyle: “God, I’d be lost without you, Tony,” Steve says, like a
confession, and his eyes are closed, leaning in to kiss Tony, so he
doesn’t see Tony’s smile stutter.It’s not that Tony doesn’t like
it- he does, but it worries him. He can’t put his finger on it, but
something about Steve saying that to him makes his stomach turn over.
Not that it matters, because if Steve’s lost without Tony then Tony’s
going to do everything to be there for Steve.

Drug in Your Veins by Raikishi: He sees Steve break, expression vulnerable for a half
second. It feels better than it should – to know that Steve still can’t
say no to him.Serial Killer!Steve who’s still fiercely protective over Tony and always will be.

Moth by @ironlawyer:
Everything they have is built on lies. Tony is addicted to the life Skrull Steve gives him.

pyrrhic victories (things better left unsaid) (series) by kangeiko:
Tony knows the best course of action is to say nothing. Opening his
mouth will just make everything worse. (When has that ever stopped him?)

Find Yourself Some Truth (Carrying the Shield) by @navaanwrites:
The incursions left something behind: A block of ice with another
Captain America inside of it – out of time and now of universe. But the
greatest surprise might be that it’s not another Steve Rogers under the
mask. Steve reaches out to Tony to help another Captain America through
the worst of waking up, but not everything is as it seems.

Tony’s Obsession by @captainneverever:
Tony thinks he hasn’t been affected by Amora’s backfiring spell but why is everyone suddenly hitting on Steve?

Only Say My Name by @sineala:
Steve’s always been capable of obsession. Maybe his friends should remember that.

The Order of Things by Fic_Request_Blog:
So…maybe it IS an obsession, but Steve has it under control. Really. (He doesn’t. And Tony is pretty a-okay with that.)

Unveil My Unsightly Heart by Mizzy: Looking over an old prototype helicarrier for its
future viability as a base for the Avengers should have just been a
routine day full of bickering and non-adventure for Steve Rogers and
Tony Stark. But when they’re catapulted into an alternate
universe – where their alternate selves are married and battling with a
mysterious threat – the two are forced to get over their differences in
order to figure out what’s going on, before it’s too late. Because
there’s more going on than meets the eye, and Steve and Tony falling in
love might just be the most dangerous thing that can happen. Not just
for one universe, but for all of them…
[Iron Man 3-compliant.]

That Boy is a Monster by mitochondrials:
Amora realizes Tony’s particular obsession with a certain Captain Rogers
far later than she would have expected. It suits her all the same.

Fixation by @kagekanecavi:
Fixation. Noun, a preoccupation with one subject, issue, etc.; obsession.
Tony has a fixation on Steve.

When I Think About You… by Ridley160:
Tony develops an unusual infatuation after he sees Steve in the stealth
suit for the first time and spirals into a sexual crisis. After months
of a growing obsession with Steve and his uniform Tony finds himself
with a pair of Steve’s finger-less gloves, and indulges in a fantasy.

Redemption by samptra: He wanted to say he wasn’t sure when it had become an
obsession, but that would be a lie. It had become an obsession the day
he had lost him. He’d lost his soul and his mind that day. No that wasn’t accurate either; he had lost his heart that day. They buried it with that patriotic hero.