Use seatguru to look up seats. AC planes now have a newer more realistic look on that site. If you fly J make sure you have staggered # seats so you face each other on the herring bone config. 6A and 6D are the most private ones on the 777 without compromising facing each other, or if you prefer to be next to each other then 6D/G are the best.

For the new 777 3-class cabin config, I recommend sitting together in the 1-2-1 config as a couple.