Definitely not a fully mind broken one of course but all one needs to do to be considered a sex slave is to be considered property, and for your primary slave duty to have something to do with sex. Have that and your basically a sex slave. Plus there are a bunch of ways of controlling people. Drugs, Mind control, coersion, force, mind control drugs from Colombia, induced nymphomania combined with chastity that they control the key too, rewards, pavlovian training over a long period of time etc...