I wish I had some advice but my own marrige situation is just as bad . No mine is worse is many ways. After 20+ years of marrige, sex is basically just something I do every few weeks, like dye my hair. Only with hair dye the process takes longer and I get results.
You may find your sub side is not something you can just keep closing the closet door on as it was in my case. If it is a true part of you and not just a fleeting fantasy it will haunt you to no end. Little by little your satisfaction in anything else will dwindle away. Not just with sexual gratification but life in general if your core needs are not being met.
Your hubby is much more open, I would try to no end talking to him, not just about wants but needs. Even if the need right now is only to explore some.
I know you said an 'affair' online or otherwise for you was not an option.
Try re-thinking that some.
It is not an affair if he is aware and you have a open marrige. If this is something you wish to do with your hubby perhaps finding a online Dom who would work with both of you would be an option.
Good Luck, I hope you find what it is your seeking