Yes, Steve was definitely a one person sort of person -- and that was a damned good thing, because so was Tony. He was generally amused about accidental shenanigans; Steve kissing other people when it was a magical accident or letting someone catch an eye full of something that they normally might not - but if anything that wasn't good natured and accidental were ever to come along, god help whoever got on his bad side. Tony could be jealous just as easily (or, perhaps, more) than the next person.
The kiss to the temple was nice, cute but also just... something that left Tony warm. Kisses from Steve always did that, but the fond casual ones always seemed best, somehow. Like it was just some kind of natural thing that Steve didn't even have to think about. He just did it because he could and because he wanted to. That sort of thing was love, right?
"Speak of what?" Tony asked, jokingly, even as he opened the door to their place, pushing it open and gesturing widely for Steve to enter first like chivalry wasn't dead.