sure, that makes sense

I do not get how it would make him feel inadequate, though. I do not get the "inadequate" part - I totally get how he might not want changes to the status quo and in general not want to expand his horizons to incorporte new realities etc... I get that.

So, "inadequate".

If a guy A with the net worth of $X has a wife B who, one day, comes to him with a cup of Sunday morning coffee in bed, per their long-standing tradition, only to announce that she has found a guy C with the net worth of $500X, and that from now on she will be with both of them, then I can see why A would feel "inadequate".

But if I, being vanilla, imagine myself in a hypothetical marriage with a guy who has concealed his BDSM predilections until recently but finally decided to practice being honest and up front, and the husband announces that he wants to be tied down, spanked, etc. OR that he wants to tie down and spank and etc. a woman OR both, then...

... I canNOT see myself feeling inadequate, I am sorry. It is so no about "inadequate". It is about something else...

So to that I would say: "Dearest H, if you still enjoy having vanilla sex with me, then great, and please find yourself somebody else, if you have not done so already, who would enjoy being tied down and spanked or tying down and spanking you, or both, and I wish you luck and hope to hear about your newfound happiness. If it has come to the point of your no longer enjoying vanilla sex with me, then we should part company, although I will still always be more than pleased to hear about your newfound happiness.

***

But I am not your husband so if you are saying that he would feel inadequate, I am sure you have good enough reasons to believe that.