After dinner, take a nice, leisurely stroll around the lagoon. You can walk into Epcot through the International Gateway and have plenty of time to find a spot for Illuminations. You could even get a treat at the bakery in France.
If you don't feel like walking into a park, you can always just walk around the lake and check out all the Epcot resorts. The Boardwalk should have its evening entertainment going that you can enjoy.
Have a fun evening and enjoy the time you get to spend as a couple!! How romantic!!!