This was a weird read for me when it came out because up until a certain point in comics lore, Steve had never been with Peggy. He knew her, served time in the war with her via retcon and she pined for him, but he never returned that level of affection. When they brought Peggy in, it was after Steve had already started dating Sharon. And so Peggy went and married someone else (Gabe Jones), and was Sharon's sister. Then ended up her aunt, then great aunt.
Here she and Steve always had a thing. It was just another example of terrible retcons. And this one doesn't make sense and is pretty gross when you think of it for any amount of time.