Hi, dcmay, and welcome.
Like you, I didn't think there would be much of interest to me as an adult at any of the Disney parks. I didn't go as a child (Disney World didn't even open until I was almost out of high school), and I figured, why go to Florida for an amusement park? We have them a lot closer to home, and less expensive, too.
So, hubby and I finally went for a wedding anniversary. I was well into middle age by then. And I totally fell in love with the place. As the years have passed, we've gone more and more frequently, until now we go pretty much every year if not more often. There are so very many attractions at Magic Kingdom that I absolutely love. Maybe you won't love them. But it's just this one day, so give it a try and find out for sure. Then if you really don't like it, next time you can insist on doing Epcot instead.
I am an introvert and have occasional anxiety issues. An extrovert friend who sometimes travels with us doesn't get this; to her strangers in the crowd are friends she hasn't met yet. I think of them more as trees, by which I mean, the crowds are part of the landscape, like the trees and bushes and flowers, etc. I do not have to deal with them. I don't even have to make eye contact. I just have to get around/past them and get where I'm going. Of course I try not to be rude, but then, I wouldn't run into a tree or step on a flower, either.
Some of the best attractions are the ones where you sort of get to be by yourself. Haunted Mansion is a real hoot and has two-person "doom buggies" to transport you past all the ghosts and ghoulies. (Don't worry, it's not very scary.) Other rides seat more than one person per vehicle, but in most of them you and your boyfriend will have a row to yourselves. And you can ask to sit at the front so you won't even see the other people riding with you. Theater experiences this time of year won't be crowded to capacity, so you can find a spot away from other people. You'll probably want to skip the parades and fireworks (crowds abound), but that means the crowds will be low at the rides and attractions.
Food prices are on a par with the prices at all amusement parks, sports venues, and movie theaters. You'll pay a lot more than you would outside the park, but it's more convenient to eat on site than take the time to drive off site. As for shopping, if you want to save money, just don't.