[Steve just needs some much needed time to himself so that he can disconnect and figure out if he eveb has a girlfriend anymore. Jonathan Byers sure did ruin everything and Steve still doesn't understand why he just didn't allow Tommy to proceed with the attack. Right, Steve wasn't that guy and deep down he knew Jonathan didn't deserve to be threatened with a knife. (Tommy wouldn't have ended it with just a loose threat and Steve knew that as much as he hated to admit it.) 

Steve doesn't necessarily think it's such a wise idea he should stay in the home of someone he still wants to royally destroy despite Jonathan's hospitality.  There is still too much tension between the two boys and Steve doesn't want to bring that into Mrs. Byers' own place. 

There is something about the way Jonathan speaks and his own mannerisms that go well past just Jonathan's typical awkwardness that seems very off and strange. Steve isn't buying a damn word coming out of the other boy's mouth and his lame attempt at lying is only making Steve that much more agitated. ]

And Nancy?

[Because Steve just isn't buying this shit and it's evident with the way his eyes narrow along Jonathan in a way that could melt the younger boy to a mere puddle if Steve had the ability. ]

I don't know what kind of stupid bullshit you're about to get yourself into but just know I'm not going to be around to save your ass all the time, Byers. And seriously? Your brother?