How should I...

You could always mention BDSM in regular conversations and see how your partner reacts as a way of gauging their opinion on the subject, but it's probably best just to be honest about it anyway.

If you put aside the part of you that likes BDSM just to avoid potential problems in your relationship you probably won't ever feel 100% fully contented with your sex life, and that discontented feeling can lead to stupid decisions like cheating.

You could try easing him into the idea. Springing on your partner that you want to engage in 24/7 power exchange can be quite a shock. Starting off with little things and explaining what you want can help make your partner come to understand your needs and adapt to them. Seeing how positively you react to their attempts may also help.

Good luck!

You could also try starting the conversation with things like "Have you ever thought about..." or "Do you think it'd be fun to..."
Like Caus said, easing them into it.