Not enough time has passed.
Mutual breakups are the mythical beast of relationships. People claim to have seen them, but any sane person knows they don't actually exist. In the aftermath of a relationship, someone is always left feeling suicidal slighted, and unresolved feelings linger long after your last belongings have been exchanged.
As an easy rule, if you've just broken up, sex is always the worst possible thing to bring into the equation. You never hear anyone exclaim, "Wow, that really cleared things up!" after humping their ex. Nope. It's all cloudy judgement and really heavy dirty talk. If "Why don't you love me anymore?" doesn't get your blood flowing, you're better off steering your sex drive in another direction.