Batman and Robin, despite the Memetic Mutation status of the idea that they◊ were◊ rather more◊. Considering the number of Robins Bruce has gone through, and the fact Batman is a Parental Substitute to most, the "life partner" part doesn't apply. A more straight example would be Batman and James Gordon, going as far back as Gordon being the first one to console Bruce after his parents' death, and Year One where they were the first true ally they had in their struggle to clean up Gotham. Gordon is one of very few people outside the Bat Family or the Justice League that Batman will trust with his life.
Cassandra Cain and Stephanie Brown when Cass was Batgirl. Stephanie was impressed by Cassandra's skills, and asked Cass to teach her to fight. The two became extremely close friends afterwards. Likewise, Stephanie was extremely close to Kara Zor-El alias Supergirl in the pre-Flashpoint universe.
Dick Grayson (Robin I/Nightwing/Batman III) has a very close friendship with Wally West (Kid Flash/Flash III) ever since they were kids. Pre-Flashpoint, he was often portrayed in a close relationship with Roy Harper (Speedy/Red Arrow/Arsenal) as well (post-Flashpoint Harper's been claimed by Dick's brother Jason).
Barbara Gordon alias Oracle and Dinah Lance alias Black Canary. In the pre-Crisis universe, Supergirl was Barbara's best friend. In DCRebirth they become friends again.
Conner: As far as I'm concerned, you're my Robin. Always will be. Tim: And you'll always be my clone boy.
After Conner's death, Tim changes his Robin costume from the traditional red and green to the more somber red and black, explicitly in honor of Conner's colors.
Tim spends a great deal of time trying to clone or otherwise revive Conner, Bart, Stephanie and his father after their deaths. He almost allies himself with Ra's al Ghul at one point in order to perfect his cloning technique.
The last thing Tim thinks of when he almost dies after being attacked by the Council of Spiders is how he'll get to see Conner again ( at this point Stephanie had already returned to the mortal coil).
This friendship is back as of DC Rebirth, where Tim stops Bart when Bart says Young Justice is back and Tim says "Not without Conn[er]"
Booster Gold and the Blue Beetle (hereafter "Boostle") of JLI fame are probably the most prominent Heterosexual Life-Partners in The DCU. One storyline in Booster's comic involves Booster time-travelling to keep Beetle from being killed; when he is told this has the potential to destabilize the multiverse, he decides Beetle is worth the risk.
When encountering former (dead) Flash Barry Allen while cruising through the time stream, this exchange occurs:
Beetle: You 'rear-ended' Barry Allen?
Booster: Oh, grow up!
There's also the scene where, after one of their "break-ups", Booster trails Ted in a public place and begs Ted to take him back.
Beetle: Get a grip, Booster. You're acting like some jilted lover.
Booster: Well, that's what it FEELS like!
Beatriz "Fire" DaCosta and Tora "Ice" Olafsdotter. It was even in-canon -mistaken- for gay when Tora was temporarily dead and her replacement, who (for some reason) looked a lot like her, misunderstand Bea's mourning. Admittedly, Bea was really off the deep end but still. The way it was written it did seem to indicate that Bea's close friendship towards Tora had sapphic undertones and that the resultant subconscious sexual jealousy was a big reason for Bea's sometimes extreme antipathy towards Tora's boyfriend, Guy Gardner. Once Icemaiden made her face up to that, Bea could learn to appreciate Guy's good qualities, and for a time the two found solace in each other's arms.
Barry Allen and Hal Jordan - theres a whole miniseries dedicated to their friendship, called Flash and Green Lantern: The Brave and The Bold.
And Oliver Queen and Hal Jordan - Issue #4 of the aforementioned miniseries had Barry jealous of the time Hal was spending with Oliver.
Hard Traveling Heroes was full of this. And it was lampshaded by Kevin Smith in his early run by Roy Harper (Red Arrow/Arsenal), saying that it was "typical Ollie, get a kid ward, train them, get close to Dinah then leave them both to go hang out with Hal". This is AFTER Queen had come back from the dead, and was brought to the afterlife to talk with Hal Jordan/Spectre to see what was up.
Jay Garrick and Alan Scott, as well as their successors, Barry Allen and Hal Jordan and (to a lesser extent) Wally West and Kyle Rayner. Maybe it's just a Flash and Green Lantern thing.
Guy Gardner and Kyle Rayner in Green Lantern Corps. So much so that Kyle's death causes Guy to become a Red Lantern.
The Green Lantern Corps is rife with this as is probably to be expected. In particular, Isamot Kol and his sector-partner Vath Sarn bicker Like an Old Married Couple and their interactions are loaded with Ho Yay.
Teen Titans: Beast Boy and Cyborg. Cyborg is often bitter at what he frequently sees as the loss of part of his humanity, but Beast Boy can always cheer him up. Conversely, when Beast Boy hits a few too many points on the dingbat meter, Cyborg can bring him down to earth.
One of the major changes from pre-Crisis to Post-Crisis is the removal of this trope from Batman and Superman's relationship. The impact of Batman: The Dark Knight Returns, as well as Character Development in the Bronze Age that had turned Batman back to his dark roots, set the stage for relatively little kerfuffle over the retcon, the reasoning being that their "true" personalities (friendly, laid-back reporter versus gruff, brooding vigilante) were too different to get along.
And now it's back to Heterosexual Life Partners status, with the launch of the Superman/Batman title.
In the New 52, they went from "distrustful, yet respecting" of the other, to actually pretty good friends. A new book, Batman/Superman, even details how they first met and shared adventures for the duo. Batman even keeps Superman & Wonder Woman's relationship a secret for as long as he could out of respect.
In the Pre-Crisis universe, Kara Zor-El and Barbara Gordon were best friends and knew each other's Secret Identity (although they didn't often team up). During the Crisis on Infinite Earths, Kara encouraged Barbara when Babs were frightened. And Barbara delivered Kara's eulogy when her friend died.
In the Post-Crisis continuity, Kara and Stephanie Brown. They love spending time together and helping each other. And if you pick on Steph, you will not know what hit you.
Kara and Wonder Girl Cassie Sandsmark were also very good friends before the reboot.
In Supergirl (Rebirth) story arc "Escape from the Phantom Zone", Kara and Barbara meet and quickly become great friends again.
In Many Happy Returns, Pre-Crisis Kara and Post-Crisis Linda become this. Linda tries to save Kara's life through a Heroic Sacrifice and has a breakdown when she fails. On the other hand, Kara openly says she trusts Linda with her life.
In the post-Flashpoint DC universe, Kara met Helena when she saved her life. Since then they became "Best Friends. Forever". When they got stranded in the main Earth, they lived together. Helena called Kara her "oldest and dearest friend".
Jason Todd and Roy Harper are this since the start of the The New 52 when they teamed up on Red Hood and the Outlaws. Despite having some obvious differences (and in Jason's case, reservations about the whole thing) the numerous adventures they had together made them inseparable.
Wonder Woman (1942): Bobby Strong and Glamora Treat spend most of their free time together, and know each other well enough that during times of crisis, like being ambushed, they don't even need to talk to each other to work seamlessly as a team.
Wonder Woman (1987): Ectreba and Sakritt were already inseparable allies long before Wondy showed up and led them in a slave revolt that ended up forcing an intergalactic empire to abolish slavery. After Wondy returns to earth, the two women remain as the captain and the captain's number two of the Space Pirate Revolutionary group that's been turned into privateers meant to prevent the return of slaver to the aforementioned Empire
Cable and Deadpool in, well, Cable & Deadpool (although many fans perceive this as going straight into Ho Yay). They are extremely close despite Deadpool's personality being obnoxious even at the best of times, and Deadpool was the first person Cable pictured/made psychic contact with while trying to decide whether to blow himself up. They were genetically commingled, so that "one phone call" would have happened even without intent....And Cable needed to make that contact to manipulate Deadpool into Doing The Right Thing.
Both C and D are well aware of their Life Partner status, especially evidenced when they both regularly called the time during a small falling out between them ("Small falling out" in this case being Deadpool's new membership in a mercenary group hired to destabilize Cable's fictional country Providence. Said membership was revealed when 'Pool shot Cable in the back of the head.) a "divorce".
Once when asked about his relationship with Cable by well-known gun-for-hire The Cat, Deadpool responded that it was a 'Don't ask/Don't tell deal'. Feel free to interpret that however, you wish.
The Cat:...don't ask don't tell? Oh...OH!
Luke Cage and Danny Rand, also of Marvel Comics, with Luke going so far as to name his daughter after Danny.
Their close friends Misty Knight and Colleen Wing also are considered Heterosexual Life Partners, with Luke Cage going so far as to recommend the two get "gay married."
When Danny is asking Luke to join his new non-profit, he says 'I love you with every fiber of my being'.
Openly mocked by Spider-Man, in an issue where Luke's wife Jessica, upon finding out that Spider-Man was Peter Parker, gushed that they went to the same high school and she had an enormous crush on him. Later, Luke is clearly in a mood and not talking to Spidey, while Spidey tries to explain that he never really noticed her and it was years ago anyway. There's a pause, then Spidey lets fly with this one: "But you and Iron Fist broke up, right? 'Cause I'd like to take a shot at that action." Luke goes from looking mildly annoyed to seriously pissed.
Spider-Man is famous for having met, teamed up with, and/or fought every hero in the Marvel Universe, but his friendships with The Human Torch and Daredevil are the closest and oldest.
Deadpool and Spider-Man seem to be heading into this territory in their recent 2016 series. Issue 12 has them spend Christmas together, and Deadpool mentions how much he appreciates Spider-Man's friendship. The feeling is mutual. They got each other gifts, and decide to open them at the same time. It turns out that got one another sweaters with their faces on them, but the faces are reversed on each sweater. They both go out wearing their sweaters, and say they ride and die together, and are "bad besties for life." Much like Cable & Deadpool, their relationship contains a bit of Ho Yay, if not more given Deadpool is genuinely trying to change his ways to gain and keep Spider-Man's respect. In addition to Itsy Bitsy, their "daughter" being created from their combined DNA. She refers to them both as "daddy."
Matt Murdock and his best friend and law partner Foggy Nelson were roommates in college and started their own law firm after graduating. Foggy has spent most of Daredevil's history as Matt's Secret Keeper, and after everyone in New York was given Laser-Guided Amnesia to forget Matt Murdock was Daredevil, he immediately re-revealed his identity to him. Notably, a guest appearance in a 2018 issue of Amazing Spider-Man shows Foggy attending an anonymous support group for the friends and families of superheroes who struggle to bear the secret alone.note Among the other attendees are Ganke Lee (friend to Miles Morales), Wong (friend of Doctor Strange), Pepper Potts (associate of Tony Stark), Willy Lumpkin (mailman of the Fantastic Four), and Mary Jane Watson (girlfriend of Peter Parker)
Foggy: I mean, he's my friend. Sometimes, I see the injuries, the wounds, and I just feel...helpless.
Supervillain example, Mentallo, and the Fixer. Though they "broke up" when Fixer joined the Thunderbolts, Judging by the MODOK's 11 mini, Mentallo stills misses the Fixer.
Fixer also seems to have this status with Baron Helmut Zemo.
Previously, villains Black Tom Cassidy and the Juggernaut.
Also Wolverine and Nightcrawler.
Also Nightcrawler and Colossus as well. Sometimes two would fight over the other like jealous girlfriends. Nightcrawler and Captain Britain too, though they didn't always get along.
Rachel Grey and Kitty Pryde are this, from Excalibur onwards, with the two usually being on the same team, rarely being seen apart for all that long, and Rachel being one of the bridesmaids at Kitty's aborted wedding to Colossus. It often drifted into Ho Yay, or a Romantic Two-Girl Friendship - they were creations of/developed by Chris Claremont, who was famous for doing a lot of both. Further complicating matters, in Rachel's Bad Future, Kate Pryde, her older version of Kitty, had been a close friend and a mentor, who sacrificed herself to save Rachel. Perhaps the crowning moments were when Rachel went into a miserable funk after Kitty got back together with Colossus in the 90s, when Kitty got ominously and angrily protective of Rachel's comatose body during the Excalibur era, and when Rachel, who thought she was about to die, hugged Kitty and tearfully asked, when she was born, if Kitty would take baby Rachel and 'give her a kiss hello'.
Magneto and Professor X: a tragic case of a broken life partnership and Depending on the Writer Magneto especially regrets that their ideologies have driven them apart.
In a similar, though more jarring sense, Cyclops and Wolverine, with their recent breakup and both sliding down different slopes. Prior to this, the two were often at each other's throats but in a manner similar to two brothers, and when push came to shove they'd be as thick as thieves. In fact, once Jean Grey (Scott's long time love and late wife, and the woman Wolverine had the hots for) died, thus removing the main source of their bickering, the two stopped arguing so much and became more openly close and friendly. Then Wolverine became a hypocrite and Cyclops became an extremist, and then Cyclops as the Dark Phoenix killed Professor X, and now the two can't stand each other - though before Wolverine died, they had it out (fought a monster, had a few drinks), with Cyclops pointing out Wolverine's hypocrisy, and Wolverine explaining this his main issue was the way that he felt that Cyclops kept justifying it/avoiding taking responsibility for what he'd done (whether he was responsible or not, on some level, is another matter, but it's a reasonable enough argument). After, they disagreed, but more amicably.
X-23 and Jubilee, the two 'daughters' of Wolverine who have similar issues. It's a tad darker than normal as it partially formed out of the two each agreeing to take the other down if they lose control.
Cannonball and Sunspot from New Mutants. The two boys quickly gravitated towards each other due to being the only guys on the initial team, and have been near inseparable since. At one point they get tired of being superheroes and break off from the New Mutants to go on a long-term holiday together, during which they're both drafted into the Avengers. When Cannonball finds himself a girlfriend there, Sunspot jokingly calls him a traitor. Then Cannonball and his wife leave to a distant planet to raise their son, only for Sunspot to show up after a few months with the (correct) assumption that Cannonball would immediately come back to Earth for whatever Sunspot has planned.
Rictor and Shatterstar of X-Force fame were this for a long time, along with that special touch of Ho-Yay, until finally the 'Heterosexual' part was thrown out.
Tony and Steve are almost in a bizarre, giant ass HLP Dodecahedron, given how many people they share this relationship with. As well as each other and the mentioned above, Tony, Depending on the Writer, has a, slightly more vitriolic, one with both Bruce Banner (one played up in the recent Avengers film) and Henry Pym, while Cap also has one with Clint Barton. Clint Barton, meanwhile, has one with Henry Pym too, making things all the more circular, while recent developments have given Hawkeye something similar with Captain Britain. Captain Britain, meanwhile, held a similar, though more aggressive, relationship with Nightcrawler, and, in-spite of introductions, a more pleasant one with Pete Wisdom.
In Guardians of the Galaxy, Rocket Raccoon and Groot. As the series went on, Rocket's relationship with Groot went from wanting The Big Guy for back up to this. And it only became more apparent after the Timely Inc. mini-series as they're currently the only active members of the Guardians of the Galaxy.
Jessica Drew and Carol Danvers. They're even approached as a pair during the recruitment drive in Avengers #2, while everyone else, except for Cannonball and Sunspot (another pair of Life Partners), got approached individually. Carol also has one with the other Jess, Jessica Jones; not surprising, given that Jones was an expy of Drew when first created.
The eponymous hero started his adventures alone, but was soon joined by Captain Haddock. It's debatable whether the two are heterosexual or asexual, though they're both definitely Celibate Heroes. This is probably due to Herge being a devout (liberal in later years) Catholic who didn't believe in including any romance in his works.
The detective duo Thomson and Thompson (Dupont and Dupond in the original French) probably count; though they look like twins, we're never given any indication that they're actually related.
Blake and Mortimer: together they fight pseudo-scientific crime... and sometimes sleep at each other's place from time to time.
In the American Civil War-set adventure comic The Bluecoats, patriotic and often naive Chesterfield tends to consider Corporal Blutch to be a defeatist coward while cynical and pragmatic Blutch considers Sergeant Chesterfield to be an obnoxious blowhard, but they are virtually inseparable from each other.
This is a rare case of Depending on the Writer in Franco-Belgian comics, as Fantasio has been shown to be very interested in girls in the earliest books, with usually horrible luck (except when using a Mind-Control Device to get kisses). Latest books have downplayed this, though. Conversely, Spirou, usually close to Asexual, has occasionally shown interest to girls.
Asterix: Asterix and Obelix show some interest in women, but it seems like they still prefer to stay single and have more adventures together. They were even born at the same time on the same day according to the short story "Asterix's birth", which the druid Getafix proclaimed to be a sign that they would be best friends forever.
If you get away from the older/younger dynamic, "Tif & Tondu", "Quick and Flupke", "Johan & Peewit" (and this last case may actually also belong to the older/younger dynamic: Johan is clearly a young squire, but Peewit's age remains deliberately ambiguous, thanks to him being a little person; he may be as young as Johan or much older)...
Even, if you stretch it a little, Lucky Luke (with Jolly Jumper).
James "Biggles" Bigglesworth and Ginger Hebblethwaite in the Biggles comics. The BBC sitcom The Thin Blue Line makes a case that Ho Yay is in the air, but Inspector Fowler, who is a fan of the books, vehemently denies it.
Everyone's favorite non-affiliated coppers, Sam and Max: Freelance Police, have something like this, more like a Batman-Robin type deal but with more...uh...affection(?) by Sam to Max, and with significantly more insanity on Max's part.
Bone: Fone Bone, Phony Bone, and Smiley Bone are all three orphan cousins who have each other's backs. Part of their backstory is that Phony Bone had been a Parental Substitute to Fone and Smiley, and as the story progresses, Phony has to learn how to treat the other two now as equals and Heterosexual Life-Partners (and occasionally Band of Brothers).
The two incompetent rat creatures, Smelly and Stinky also qualify due to the fact that they are often seen together and address each other as "comrade". Their bickering is mostly similar to that of an old married couple.
Surprisingly for a Porn with Plot series about sex-positive women, all of the women in Kevin J. Taylor's Girl series fit this trope rather than the expected girl-on-girl action, specifically between main character JalieraDane and JessieJames, and to a lesser extent, Jill with either woman. They've shared the same men, casually slept naked together in the same bed even without men and showered together, but not even a flirtatious word to each other. Jessie even lampshades how one of the guys expected took pictures with her camera hoping to catch this just because she and Jill were showering together when there wasn't even any "skinship" going on.
Jessie: Those pricks came into our bathroom and shot us in the shower. I guess they were expecting some kind of lesbian shit. Assholes.