This Achievement is very tricky but is obtainable in the very first Mission. Once you get to the Alter if you look to your right you will see a box full of objects, inside is the ring. Grab it using
then position yourself in front of the alter, use the
to swing the ring towards your bride to be and hit
to release. If done correctly the ring will fly on to your brides finger and pop the achievement.
This took me around 20 minutes to do and can be very annoying, if you get the ring on her finger and don't get the achievement, you're too close and need to restart the game.