Steve and you loathed eachother for the first few years of Hawkins high, but you two were forced together by some twisted trick of fate; after the revelation of the upside down and the monsters that lurked in Hawkins, you and Steve grew closer- particularly because you two were one of the only people who knew about the upside down.
Now a monster, Vecna- who had previously gruesomely slaughtered Chrissy Cunningham, a cheerleader- was after you, and nobody besides Eleven had yet escaped Vecnas grasp.
Vecna was cruel in the way he picked his victims, he would pick those with a painful past that still haunted their present, and he would make them relive it before claiming their lives. Unfortunately, you had already re-lived your past in one of Vecnas visions a few days ago- which is when you realised he was targeting you; though, you'd been saved from the nightmarish vision by music- which kept Vecna at bay- for now...
you were in the Mikes basement, and the group- Dustin, Mike, Will, Steve, Max, Eleven and Nancy- wanted to keep an eye on you to make sure Vecna didn't come unexpectedly, so they were taking shifts in staying awake with you, for your protection. You decided to write letters to everybody while you still had the opportunity, unsure if you could escape your fate and live. When Steve awoke for his shift to stay awake with you, you gave him his letter- which you had written before anyone else's. "whats this?" he asked, confused. The second you explaining that you only wanted him to open it if you died, he shook his head and gave you the letter back "no- no. You're not dying, okay? I'm not- I can't lose you." he blurts out.