You know what your boyfriend's personality and what he is interested in. Use the boards or recent version of The Unofficial Guide to Walt Disney World for suggestions.
My number one recommendation is to use a touring plan to maximize your experiences while minimizing your time in lines. You can find touring plans on the boards, in the Unofficial Guides, or through services like Tour Guide Mike.
In my case, I took steps to avoid our time-consuming (but very polite) arguments:
"What do you want to do now?"
"I don't know. What do you want to do?"
First, I made a plan suggesting what days to visit what parks and water parks. She accepted this readily, especially once I described Extra Magic Hours.
Second, I insisted on a plan of attack for the first handful of attractions at each park, so that we would best avoid long lines. She wasn't happy with my commando tactics until she saw the results: "OMG, Tower of Terror has a 75 minute wait and the FastPasses are gone? I'm so glad we followed your plan." Yes, I took credit for the Unofficial Guide touring plan. Just call me Dr. Evil.
Also, don't forget to allow for spontaneity and flexibility. Some things cannot be helped. Like when I caught a 24-hour gastro-intestinal bug. There was no way we could follow my theme-park-commando plan that day.