While he is in business meetings during the day, there are a bunch of things you can do! Like everyone said, shopping, museums, etc.
The Architecture Foundation does walking tours around the city, Chicago has some very interesting architecture, so I would definitely recommend those if you like that kind of stuff. http://www.architecture.org/
The Historical Society also offers tours, but I believe most of them are on the weekends... so hopefully your SO won't have meetings then :)
The Wendella river boat tours are another great option.
Personally, I don't get the appeal of Navy Pier, and probably never will... maybe if I had little kids, I guess. However, there is a great Shakespeare Theater there, and there are evening cruises that take you out onto the lake for great views of the skyline at night. Also, on a Saturday night you would get to see the sky line and the fireworks which are every Saturday - or Wednesday (I think) - night from Navy Pier.
If the weather is nice enough, check before you head over here, you can always relax and get some sun on the beach too!
I don't want to repeat what others have said, you have gotten some good suggestions :) Oh, and another place for you to check for things going on before you arrive in Chicago is Metromix.com lots of listings of events, restaurants, etc.
I really loved the architectural boat tour. And we ate at the original Uno's. Also, Michigan Ave shopping - had food at a great Italian place across the street from Chanel, can't remember the name now. Art Institute is a must see and the Bean sculpture is really cute. Great city.
Also, if you want a classic Chicago experience go to Gene and Georgetti's. I pratically grew up there! My mom created "Chicken alla Joe" and we named after our fave waiter who always took care of us!!!
Is it humid in Chicago in the summer?? I just moved there in December from the Houston area and I had the impression it wouldn't be nearly as bad as down there... please tell me I am right..I was looking forward to not sweating my way through summer.
My Dh and I went to Chigaco Last september for a week! WE LOVED it!!! WE stayed in The Loop at the Palmer House Hilton. I had so much fun eating all the Delicious Pastas and Pizzas. And there are tons of shops, museums you wont be bored~
And I have officially fallen in love with that city. It's beautiful.
The one thing that I remember so vividly is when I was on a boat tour of Lake Michigan and the Chicago River. The view is incredible. As we passed the buildings while on the river, that's the moment where I fell in love LOL. I didn't want to leave Chicago and I can't wait to go back to it!