Steve Rogers just said fuck. Tony looks a little like he's having a harder time processing that than the rest of the conversation.

"I. Sure?" He says, once he's shaken his head to clear it. "I mean, all of my experience with guys is years old at this point, but it's not exactly the kind of thing you forget." And sex with Steve is...not something he can see himself turning down. In this context or out of it.

Though that does bring something else to mind. "So if this is a sexual thing...and a recurring thing, I think?" His tone lifts at the end to make it a question, but it's more rhetorical than not. "How exactly would we be defining this relationship?"

He's a scientist, he likes having names for things. Sue him.