I don't see it. I'm honestly not trying to start an argument, I really just don't see it.
And I don't know what I've missed that convinces you all that they did.
If they had sex then he either remembers or he doesn't.
If he remembers, why is he an asshole about it in front of Mia? And also tell her he doesn't remember in his bed?
If he doesn't remember, how does he even know he had sex? And, why is he allowing Mia to be intimate, without saying 'Woah, what ya doing?'
The conversation about not complicating, does hint at it, but doesn't answer or override the questions above for me (and could just as easily be Mia wanting to be more than friends, again IMO). Is there something else?
It also appears that I am in the minority thinking they haven't, so I'm really confused as to what I have missed. I'd love it if anyone can enlighten me as to why they're convinced it happened.