For the most part, you perfectly understood what was happening. You knew that you were in a spiral of arousal and denial that you had created. You knew this is what it would be like. Or at least, you imagined it might be something like this. You didn't know how quickly it would build and overtake you, but you weren't upset. You were frustrated, but you were ridiculously horny, which is exactly the fantasy you had asked Nikki to play out for you. But there were two key elements that you did not expect.
First, you were realizing that a tease and denial experience was vastly different from a tease and denial fantasy. In the comfort of your apartment, you would strip down, get comfortable, watch some porn, get your self to the edge a few times then stop, to simulate a tease and denial experience, then usually watch some video where a real dominatrix was giving a real experience to a real dude, and then blow your load all over. It turns out that those chastity belts are pretty damn good at what they do, which is deny any orgasmic pleasure. You have as vivid an imagination as the next guy, but even that doesn't stand up against actually feeling the friction on your cock driving you to orgasm.
Second, you did not expect to completely forget about fucking Nikki. It was absolutely the furthest thing from your mind. Maybe it was because she hadn't really teased you with that yet. Maybe it was because you were so fixated on eating her out and imagining what her underwear looked like. Or maybe it was because she was so damn hot that sleeping with her didn't even seem realistic. Well, maybe that wasn't exactly true. She was definitely out of your league, but you weren't some hideous troll. You worked out, you did have a 7 inch cock - you know, when it wasn't locked up and could actually grow that long - and your ex girlfriend was also smoking hot.
Ahh, your ex. This was the first time you had thought of her since you met Nikki.