Getting into some bondage, tied my best friend up and put on a show with his girl [Bull’s perspective] [humiliation]

I’m in this arrangement with my best friend and his girlfriend for almost 8 months now. It’s been a really wild ride and I’ve kept posting abt the experiences regularly.

Now this happened some 2 weeks ago and this was the first time we went into some bondage. This idea came to us when he once told he orgasmed just by watching us, with barely touching himself. We met as usual after a hectic day’s of work, went out for dinner and we went to their apartment.
We started making out as usual, slowly stripping each other…my friend as usual sat in his chair and was watching us.
He stripped down to his underwear and then I tied his hands back to the chair, there was a tent in his underwear already. Then we just left him there and went on to the bed.
His girlfriend, as usual, was wild. We kissed, got naked, we went down on each other….and of course we were telling my friend how hot it all was.
I’ve slowly gotten comfortable passing sly insults at him too. Like how he could never experience the real depth of her pussy and all. Even she, has got extremely comfortable comparing our sizes and letting him know.

We got into our usual position, doggystyle facing my best friend so that he could see how much pleasure we give to each other…5 mins in, he cum in his underwear listening to his girlfriend moan. And 10 mins later, he was hard again listening to his girlfriend orgasm. As I came close, we got off the bed, she kneeled beside him and I cum on both their faces.
He remained tied for a long time until his arms started to hurt.
I’m starting to enjoy this humiliation thing more and more. She has been suggesting abt me spanking both of them red, something that I still need sometime getting comfortable with lol.