One should note that Cloud isn't even the real Cloud while he's with Aerith. He's a fake Cloud, and the smile is symbolic, yes, but it wasn't only her who helped him move along. It's stated that, "Tifa is the catalyst to Cloud", meaning she's his 'strength,' which shows enough in my opinion. Of course Aerith helped a large role into getting rid of Cloud's guilt, but that was because he felt guilty of her death. Obviously the only person who could actually help him was her. And not to mention he felt guilt for Zack too, to which who Zack...In the game the only time Cloud laughs is when he is with Aerith after they escape the Turks from Aerith's church and when you see him smile at the very end of Advent Children it's when he sees her. I know the smile in Advent Children Is symbolic of how he can finally move on and lose his guilt ect but It was thanks to her in my opinion.
got extra screen time and is shown helping Cloud move on
And Cloud smiled to BOTH Aerith and Zack. Not only Aerith.
Awkward? Oh yes, very much. I can just imagine Cloud screwing up if he ever asked Tifa to marry him (which he probably won't, but ah, one can dream).I know it was never going to happen in the first place and that the Cloud and Tifa's relationship has more evidence of being present in the “On the Way to a Smile: Case of Tifa” and in ACC. Despite this they still have a lot of difficulties and awkwardness to get past but I think they'll make it there.
Cloud: Marry me Tifa.
*drools*