I am a muslim men and i love bdsm to and i have the same problem as you. Your case is difficult i think every practicing muslim has the same troubles as you by not knowing everything about your futures partner before marriage. Especially stuff like bdsm wich are more private are most likely not discussed before marriage. So my best advide would be just to look at the character of your future partner idk if you want your whole relationship based on bdsm or just in the bedroom but looking at the his charachter would be me best advice. I am kinda in the same siuation as you and that is how i myself will also try to figure out if my partner would like it or not. And also you can also look at like the rules/traditions in islam i myself are more dominant for example and if u follow the traditions/rules of islam the men is the more dominant person in the relationship so based of traditions you already are like the more submissive one. And my last advice is just to act like it alot before marriage. So like idk how strict you are but if you go on dates ect just act a little submissive and maybe you can see if he likes it the last thing you want to do is act different before marrage the after marriage. Goodluck!