Your girlfriend had a strong fascination with lamias, who were creatures that were half women, and half snake. Their tails were so long, that can wrap around anything such as a human being, and might have more than enough organs to breathe, and eat more than snakes. Of course, she decided to turn you into that.
You felt your own body begin to shake, while your clothes shattered apart, and leave you naked, while your own penis began to get erect, and spill out cum. Your penis shrivels up, with your cum making a big mess on the floor, as a hole opened to become a pussy, while your butt began to inflate abruptly. Your girlfriend noticed some green scales grow on your legs, while your arms became female length, and all the body hair fell off of your body once more scales covered your legs.