hi cicily and welcome cicily, i hope things may improve for you in that area,

everyones different i know but unfortunately ive always found in r/ships (mine anyway) that those who call bdsm sick and twisted never really change their opinions that much, it often shocks, them scares them and is too much unknown and all too often those who are scared of the unknown dont want enlightening when society teaches them something is wrong it becomes indoctrinated and it not always that easy to show them it isnt.
but thats only my personal experiences, maybe your partners different.

just a thought but instead of concentrating on BDSM have you ever told him you prefer the more traditional roles in r/ships? more of a deferring to him as he's the man of the house,

just in small ways to begin with perhaps when hes ready to bathe you could just go run the bath for him,ask if its the right temperature and such,offer him masages when he's tired, ask him if things are convenient rather than saying you need to do for eg the shopping a hairdressing appt, encourage to help choose you clothes etc?...thats if you dont already.

leave the kinky stuff out for the time being, im not saying it will work although i alway found that men tended to actually prefer it that way, it was the sexual side that didnt change other than a few mild kinky games,

if there isnt at least a tiny spark of interest lurking around to begin with its unlikely there ever will be..if somethings not there its just not there, when a sub doesnt have the slightest 'Dominant' bone in his/her body thats never going to change and i guess you could say it's the same principle really

and in all fairness to him you cant try to force him to.

just my (long winded) ramblings sorry!

i know how frustrating and lonely it can feel and i do hope things work out for you...maybe he's just not noticed that 'spark' yet