When it comes to Steve Rodgers...

[justanotherclassic]

Sharon and Peggy technically were introduced in the same issue, with Steve being morose about a WWII fling (Peggy) and then meeting a woman who looked similar (Sharon). Peggy wasn't really a major character and really only existed to fill in the backstory for Sharon, who was the main love interest until she was fridged, and later once again became a love interest (will they/won't they) until Brubaker hooked them back up. They've been going strong since. Prior to the MCU, I would argue that Peggy was more or less a footnote to the lore.

[GenericUsername]

It's Sharon. Peggy was Steve's love in WW2.

Not really. His love in WWII was Betsy Ross. Peggy was a mere kiss. And that was a retcon.

[Oberon]

Is the Betsy Ross also the Sun Girl character? (and theorized as an aunt or something to Thunderbolt Ross at one point.....) ?

Also Captain America(s) after WW2 approximately are not Steve Rogers. They were replacement whose names I don't remember, but had previous been other heroic characters during WW2. there were at least 2.
As that is a retcon, it is retcon'ed that this Betsy Ross/Sun Girl was hanging around with one of those Caps.

[Oberon]

I so stand corrected! She is Golden Girl, this Betsy Ross. But the retcon stuff was right.

[John Venus]

yeah I like the coupling so I'm glad to see they've lasted a while. When does Peggy appear? Was she around in the Golden Age?

I think this breaks it down well:

https://www.vulture.com/2015/01/agen...ey-atwell.html

IIRC, CBR also did a run down on Peggy's comic book history including the stuff with Gabe Jones and Dr Faustus but I can't find it.