Why? Because, first of all, Corrie can't be seen to encourage illegal behaviour. If the wedding did happen, they would be found out, Graeme would be off to jail and Xin would be on a fast boat to China. Second of all, I think Graeme is too honest to go through with it. And thirdly, I predict that Xin will get a legitimate job at the last minute, eliminating the reason for Graeme to marry her.
We know that Graeme and Tina are going to pretend to break up but will also break up for real. I expect that they will and Graeme will likely just move away or maybe go with Xin, having developed feelings for her.
What do you think? Good theory or rubbish?
