That's not NTR if they're basically both MCs, but you'll have to add the multiple protagonist tag. A lot of people like to self-insert though, so adding more than one protagonist is gonna narrow your audience a decent bit. I personally wouldn't have played this game if I knew you were planning more than one protagonist. I admit it's a silly reason to not play a game, but there you have it.
If you decide not to do the multiple protagonist route, it's NTR only if Chloe or whoever else he gets involved with is a possible love interest for Steve. You'll definitely have whiners because Chloe is probably the best looking model in the game, though.