Jonathan became distant when he and the Byers moved to California, he never called or sent a letter to Nancy. According to Jonathan, there's hotter girls in California, and when he wants to break up with Nancy over a piece of paper Joyce doesn't allow it. Jonathan booked a flight to Hawkins to break up with Nancy, breaking her heart.
Nancy loved Jonathan, it broke her heart when he broke up with her, but when he did break up with her she and Steve got closer. He ended up moving in with the Wheelers after a while because of his abusive parents. When Keith wouldn't stop talking about Nancy they made a plan, they would fake a relationship.
Steve loved Nancy still, but they were only faking this relationship, yet he still loved it. When Keith finally left Nancy alone they stopped faking, going back to just friends. When Max gets possessed by Vecna his new priority was to make sure everyone was safe. No matter how hard he tried he couldn't do much, then one night, when they went to the Upside Down Nanch got possessed by Vecna when leaving. Steve can't lose her, they only kissed a couple hours earlier, he had to make sure she really liked him and she didn't just kiss him because of what he said about that dream.
Will everything work out as they hope?
Will everyone survive?
Will Hawkins be okay?
Will Steve and Nancy get together?