Warning! Spoilers for Captain Marvel #26 below.
In order to protect a young hero in Marvel's dark future timeline, two Avengers just broke up. In Captain Marvel #26, Carol Danvers just broke up with James Rhodes AKA War Machine, so that his daughter that she met in the future, Carol Rhodes, wouldn't be wiped from existence.
In Kelly Thompson, Lee Garbett, and Antonio Fabela's Captain Marvel run, Carol Danvers was transported into a future Marvel Universe, that was ruled by the half Asgardian/Atlantean Ove. The villain intended on using Captain Marvel's powers to time travel back to the present timeline. In order to fight against Ove and save the heroes he captured, Carol teamed-up with a group of future heroes including Rhodes's daughter, Carol Rhodes, Thor's daughter Brigid, Hazmat, Emma Frost, and a slew of other young heroes who lived in the dark future. In Captain Marvel #26, the Avenger frees the future heroes and returns to her timeline - but makes a shocking confession to her longtime lover.
After returning to her New York City apartment, Danvers has a heart-to-heart with Rhodes. She tells him that she met his future daughter, telling him that she was incredible, proud, smart, and strong - all the best qualities of him. However, Carol reveals to Rhodes that the child wasn't hers and that she believes if they continue their relationship then there's a good chance Carol Rhodes will never exist. Rhodes is confused that Carol would break up with him over a future that "might not even happen," and leaves. Carol says that when she meets her, "you'll understand and you'll forgive me."
It's an understandably tough pill for Rhodes to swallow. He loves Carol and wants to be with her, but the reason she says they can't be together is that she wants to protect a future that he's never been in and a person he's never met. It's confusing and frustrating - but Captain Marvel doesn't want Carol Rhodes to not exist, so she sees this as the best path to making sure she's not erased.
As far as heartbreaks go, this is one of the tougher, more complicated breakups in Marvel history. It's impossible to say if the dark future timeline Captain Marvel was a part of will ever come to pass, but if there's even a small chance that it does, Carol doesn't want to be responsible for erasing Rhodes' daughter. Danvers' friends aren't going to allow her to wallow in sadness, as the series next issue teases the hero before forced to do a superhero version of speed-dating to get over War Machine. Captain Marvel #26 is in stores now.