I'm not trying to be mean here, I know it's your honeymoon, but it's 12 hours. Do you have that much separation anxiety that you and your husband can't be in different parts of the cabin for 12 hours? If you're going on honeymoon, you will have days or weeks together. After the honeymoon, you will have years together (hopefully). If you're gone for a week, that's less than 10% of your total holiday that you're separate for. If you base it over a year, it's less than 1% of the amount of hours in a year.
If it's really important that you both sit together, pay the fee, otherwise it will eat at you. Don't let the fee get in the way of a wonderful honeymoon.
And, most importantly, have a great honeymoon with your husband!
Let us know what you decide to do.