So after looking at the Peggy Carter page, the whole subject of the two timelines she exists in came back up and caused me to really have to think about it again, even though it's been a year since Avengers: Endgame was released.
From evaluating all the confirmed dates or placement of events in her history, I feel like that the definitive history of any possible timeline that exists is that Steve Rogers was always Peggy Carter's husband.
And this is not just a poetic or sentimental thing where "it was always him", I actually feel like there is no way it couldn't have not been Steve all along. However, it's still not a complete or confirmed idea, but from everything I've considered, this seems to be the only answer.
Here's a rundown of Peggy and Steve's history:
Captain America: The First Avenger
-Steve and Peggy meet and develop an attraction for each other
-They kiss, good things are seen for the future of their relationship
-Steve crashes into the ice and Peggy is devastated :(
Now, by the wiki's decision, which is very thought out in terms of timeline stuff by some incredible users, season one of Agent Carter takes place after TFA. Also, everything in the MCU is canon, so yes, everything in Agent Carter is canon, which I feel I need to clarify as some believe that some things aren't canon.
Agent Carter (season one)
-Peggy goes to work at the SSR, where she is hung up over Steve (true love and all that)
-By the end of season one, Peggy pours the last sample of Steve's blood in the water, saying goodbye to him
However, I feel like this isn't a "goodbye" to get over Steve, I think it was just destroying the last thing left of Steve, which would be very hard for her. This was probably known already, but some may have seen this as Peggy completely getting over Steve (hence why they open up other romantic interests for her in the next season). However, even if Peggy came to terms with Steve's "death" and moved on, I say that she was undoubtably still in love with him.
If someone you love dies, you then don't love them anymore after you accept it. "Hey, I'm your loved on back from the dead!" - your not going to then tell them to go away, as your love doesn't just go away. So, Peggy at this point would immediately be with Steve if he were to come back to her at any point. And as we see in the future, Peggy still has her feelings for Steve.
Agent Carter (season two)
-From what I recall, Steve is not even mentioned at all this season
-Peggy is faced with two possible love interests: Jason Wilkes and Daniel Sousa
-At the end of the season, Peggy kisses Daniel and it is believed they end up together
Unfortunately, Agent Carter was cancelled after its second season, so we never got to see what happened afterwards (hopefully Daniel appearing in season seven of Agents of S.H.I.E.L.D. will fill in some blanks).
From this point in the context of the show we are to believe that Peggy and Daniel live happily ever after. And this would completely work... only it doesn't... because the rest of the MCU.
So, according to this wiki (which I also agree with), the One-Shot takes place after season two of Agent Carter (but I'm not going to get into that as it's a whole other massive discussion). However, even if it doesn't (it does say "one year later" in regards to the events of TFA) then in terms of Peggy's love life, it still works.
Marvel One-Shot: Agent Carter
-Not much is shown about Peggy's at-the-time state about Steve, but either before of after her series, it's fair to say that she still loves him.
So under the assumption it's after the series, Peggy is no longer with Daniel for whatever reason (counting on you AoS to provide answers). And even if they didn't break up, they will eventually, as Daniel was not saved by Steve in the war, nor was he with he by 1949 (which I'll get to).
So far, we are at least at 1947-1949. And going along with the main idea: Peggy is single, and is about to start S.H.I.E.L.D. with Howard, and still has love for Steve.
Now, I'm sorry if this is getting confusing (or will), it is never simple when discussing time travel, but I'll try to keep it clear.
Here's what can be taken about Peggy's history between 1949-1970:
-In 1949, Peggy is living alone in a house, willing to be with Steve if he were to somehow show up at her door (what are the chances of that, amiright?)
-We are to understand that at some point she will marry a man that Steve saved, and have two kids with him.
-In 1953, Peggy is interviewed about Steve where she talks about this, as well as gets emotional talking about Steve
Now this is a problem with Steve having been her husband all along, as why would she still get so emotional about Steve "dying" if she knew he was alive and married to her? Well, one thing is maybe I'm wrong (and I could be). Another is that that specific event is still very traumatic for her (which is understandable). Someone dying, even if it is later revealed that they are fine is still emotional.
However, aside from that, we understand that by 1949, Peggy is single, as when Steve arrives from the future, they just get together. She wouldn't be dating a guy and then dump him immediately upon only seeing Steve, there would be some other stuff that would go down. And the Russo Brothers have said that they see that Peggy opened the door and immediately danced with Steve, so that clears up that.
So, by 1953, if Peggy was actually with someone else, she would have had to met him, married him, and had two children, all within 3-4 years (which could happen, but isn't the most likely outcome). So, if she was reunited with Steve in 1949, that would clear that up and make sense, as they were always in love.
In 1970, we see in Peggy's office that she has a picture of Steve on her desk. Now by that point whether it be Steve, Daniel or any other man as her husband, it would be a bit odd to have a picture of a man you knew decades ago on your desk over the person you are married to or even any of your children she would have had by then. So, that's a pretty strong reason to think that Steve was always her husband.
However, there is big issue with the fact that Sharon Carter exists. We understand that Sharon was very close with her aunt, who had a major impact on her life, so it wouldn't make sense how she wouldn't think that her uncle looked exactly like the man she would later spy on and then kiss... unless there is some weird thing that Sharon is in to. Although, my reasoning for Sharon not knowing Steve was/would be her uncle is that Sharon was probably born around the 80s, so Steve would have been, and likely looked, old enough so she didn't make the connection.
And we could probably assume that Steve chose to go under a new name, and they came up with the "Captain America saved my husband from the war" story to avoid questions about Steve being alive somehow (which still raises questions, but let's just leave it with Steve and Peggy's relationship).
So essentially, we can determine that since 1949, Peggy has been with Steve and they had children together, and Steve probably stayed hidden (never seeing Howard etc.). Now, when it gets to when we see Peggy older, she is in a retirement home and has Alzheimer's disease. However, as we see at the end of Endgame, Steve would live on to 2023, so where would he have been during this time? Not sure, maybe he was there too, and avoided when his younger self visited. Also, because of Peggy's illness, she could possibly forget about her time with Steve, so it makes sense that she would have her reaction to seeing young Steve.
Then of course, Peggy passes away in 2016, but Steve will live on, and likely is still alive currently within the MCU. So, when young Steve goes back in time to be with Peggy, old Steve sits on the bench, completing the cycle... as it also begins,,,
And of course, there is the problems with the time travel logic. As the rules of Endgame would have us believe - "Changing the past doesn't change the future" - which means if Steve changed history to be with Peggy, it would exist in a different timeline. However, we see Steve exist in the main timeline, so that would mean that Steve was always the husband. I know time travel is confusing, and there is no definitive version of it, even in the MCU, but I feel like it works, as we've seen this kind of time travel paradoxes in other movies/series (Fry being his own grandfather in Futurama comes to mind). So, when Steve arrives in 1949 at Peggy's house, it is not a new shift in the timeline, it is something that has always existed, therefore nothing is being changed.
Now of course, this isn't 100% confirmed, but I believe it is the only viable answer, as well as being supported by the writers of Avengers: Endgame, Christopher Markus and Stephen:
"Chris and I are partial to the idea that Steve is part of a strange, unique time-loop where he has always been there. The husband that you very purposefully did not see at Peggy’s bedside in Winter Soldier is Chris’ Steve. We have always thought that he was her husband. The movies you have been watching follow a line where he always goes back. To be fair, not everyone agrees with us. I don’t even know if Marvel agrees with us. But that’s what we think.”
While this topic has been discussed, and this is not a new theory, it kept running through my mind, and I had to discuss it. Sorry for it being so long. Let me know if there is anything I have left out or anything that may contradict this from being the most likely case.
