So far, I'm taking him to this sushi and hibachi place he likes, and I'm making a 280 page sketchbook full of art relating to our relationship, inside jokes, stuff he likes, and other stuff. Is there anything else I could do?
The sketchbook idea is fantastic, and probably the best gift you could give. Anything you make is worth more than anything you buy. If you really want to do more, I'd suggest preparing a way to relax after ur hibachi night. i.e. pillow fort at home to watch movies in