My girlfriend meets my coworker and i end up fucking him.

My coworker is a stretched out suit and tie who's smart. i ask my girlfriend to help me play a joke on her and think that she is going to meet her to fuck. she is stunned when she realizes it's me. what my girlfriend cannot find out is that we end up fucking on the office table and that i never enjoy her as much as with my partner's cock in my ass.