To his conscious mind he hasn't really had time to miss Tony, or anyone for that matter, but there's a part of himself that is still aware of the passage of time and his answering smile is fueled by that subconscious awareness. He's really missed Tony and that's messing with his head.

"If I stipulate that you stay on this side of the wormhole will you do it?" He's hoping, but he has to admit to himself that most of his thinking about Tony and wormhole involve Tony barreling on through because it's cool.