Version 1.07 introduced a change where friendship levels that have been "maxed-out" no longer decay. For the marriage-eligible villagers, the last two hearts are disabled until you give them a bouquet. Do you need to give each of them a bouquet and then get them to 10 hearts or is 8 hearts and no bouquet sufficient to prevent friendship from decaying?
I'm guessing that since your spouse doesn't like you giving gifts to the marriage-eligible candidates after you're married, you'd have to get those villagers to 10 hearts before you're married, if the decay didn't stop at 10 hearts.