New Inquiry Regarding Nonsexual Bondage and Friend's Situation

I’ll start by saying I’m here representing a friend (seriously). I’ve agreed to help him with some research since he’s worried his wife might find out. Let me outline the situation: My friend is interested in nonsexual bondage for women. I know this site might not be the perfect fit for questions on that topic, but if I can’t get any answers here, please direct me elsewhere more suitable. His wife enjoys bondage too, though hers is sexual, and she struggles to distinguish between the two. She has trouble grasping his desire to tie up women without being sexually aroused by it. He believes he’s unique in this regard, but while I haven’t met anyone exactly like him personally, I think that’s quite rare. Secretly from her, I’ve been assisting him as he explores this interest. Until recently, he hadn’t really indulged much, and we thought the more he understood his own feelings, the better he’d be able to explain them to her. I feel he has made small steps in helping her understand, but we both know she trusts neither our words nor those of him as a friend or husband. She will likely convince herself that he is cheating. So we have started seeking out like-minded individuals whom they can meet or speak with as a couple, whether online communities or other similar venues, to help her see that he isn’t just using this interest as an excuse to stray.