I like the story so far but I would like to see where you go from here.  Personally, I would love to see her dominate him more.  Using him as a tiny human loofa.

Good start. I'd like to see some breast stuff, since you asked, but if that's not your thing you can take the story anywhere you like.

This is a pretty decent start with some real potential, and I totally encourage you to continue. It's nice to see some writing in the first person (not as easy as some think). For constructive criticism, I would encourage you to take more time in developing the setting and characters. Instead of stating "My girlfriend is drop dead gorgeous", try using a scene to describe how she's gorgeous, without necessarily stating it.

Don't be afraid to use extra details, describing the scenes as you go. What does Jeff see, taste, hear, smell, feel as all this is happening? What emotions are running through his head from all this? Readers love this sort of stuff, and I have a feeling you'll be able to deliver.