phish

You need to make sure you've covered all the general marriage requirements, including:

-owning the largest upgraded form of the house (you do not need to have the bathtub installed)
-having purchased all of the items from the TV Shopping Network
-the blue feather (you can buy it at the grocery store)

(check FAQ/Walkthroughs for possible others...I do believe that's all you need, though)

If you've got those covered, propose to him with the blue feather (use it like any other tool by standing next to him and pushing B). Seven days later and you should be hitched! :)