I am going through this process in reverse, going to america.

In terms of how did you meet, we stated that we met on a social networking site (which this can be considered as), and have innocent photo's of us together etc. It doesn't change the fact that I am still a little nervous regarding getting asked that question at the interview.

In terms of showing communication, I would suggest sending the occasional vanilla email to each other, that you can show immigration officials. You should not need absolute proof of relationship from day one (say you deleted it or whatever), you mostly just have to prove the legitimacy of your relationship and in the case of US immigration that you have met in person within the last 2 years (i.e to include plane tickets, boarding cards, passport stamps etc)

Personally I would try and focus more on the relationship side, than the nature of your relationship specifically, but it is important not to lie, and jepodise everything.

Regards,

Arch