I've told my closest friends that I have a waifu, partly because they knew about waifuism beforehand, but also because I didn't want to feel as though I was hiding anything from them.
I've felt better about my relationship with her, and myself, since I told them. They were quite accepting of it. I've since felt more comfortable displaying my merch of her and having wallpapers/screensavers of her. I probably wouldn't have bought the daki I now own if it weren't for that, as well.
It sounds as if your friend will be happy for you as well. Good luck if you do decide to tell him, from my experience it felt like a weight off my shoulders.