It's not entirely impossible that they're interested in BDSM but too afraid to admit it.

I mean, I can understand why it would annoy you and I don't think you're taking it too seriously at all, but there is more than one possibility here. I've been an abusive relationship before too and it was horrible, I'd never wish something like that on even my worst enemy - but that and BDSM are very different things, and if that's what they're referring to then I'd say go for it because it's actually very fun and fulfilling to devote your life to someone else like that.