Be an active recreational partner.
While dating, you probably hung on his every word while he talked about those things that interested him. It was part of your charm and why he found you so darn attractive.
Bringing that when-you-first-met-magic back to life can be as simple as taking an interest in him. (It’s sad that we lost interest in the first place, but that’s neither here nor there.)
Take the initiative and plan something he loves to do. Simple things like going to a sporting event together, camping, or just sitting and enjoying a television program he likes.
It’s not what you do together rather that you’re doing it especially for him that will make him feel special.