Sharing a night with my girlfriend, and sharing her too [BDSM]

We've been living in our little Scottish flat for a few months now. We were as happy as could be.

We planned to have a romantic New Year’s Eve. I told you I had a surprise planned. You told me the same. The night came and we exchanged surprises. We were both in the living room. I took you by the waist and pulled you into me. Although we were both fully clothed, you could still feel my big, rock hard cock against your stomach. I kissed you deeply. You let out a little moan. You pulled away to show me your surprise. You slowly unbuttoned your blouse and your jeans to reveal black lace lingerie. You left your clothes on and motioned for me to 'come hither'. I moved in to take your clothes off the rest of the way. As I slowly removed your blouse, I placed my lips on your neck. Kisses went from your jaw down your neck, to your collarbone. I slid off your jeans and whispered into your ear "time for my surprise." I locked your hands behind your back with fuzzy handcuffs and pushed you onto the sofa. You squirmed and squirmed but you couldn't get out of them, as if you wanted to. I looked out of our window and gave a nod. Suddenly, you could hear footsteps, many footsteps.