"Doctor Faustus" treats sexuality with a moral ambiguity designed to produce both comic effect and a reflective discomfort amongst the audience. It's unclear, for example, whether or not Faustus' relationship with Mephastophilis (Lucifer's servant) is sexual or platonic in nature. The relationship between these two characters is further complicated by the fact that in more recent performances, Mephastophilis has been played by a woman whereas traditionally the cast has been all-male.
Some critics argue that the play reveals strong homo-eroticism, perhaps related to Marlowe's own sexual life. It's possible that the relationship between Faustus' and the demon Mephastophilis represents a relationship between Marlowe and a male sexual partner.
Finally, "Doctor Faustus" treats sexuality as a grave and powerful tempter. In the play, Faustus wastes the special gifts and knowledge that Mephastophilis bestows. He chooses instead to engage in pranks and random sexual encounters. While Faustus enjos the carnal delights to the fullest, in the end he's left feeling empty and remorseful. As he is called into hell to pay his end of the debt (he had promised his soul to Lucifer in exchange for those gifts and knowledge), he is filled with dread concerning the ultimate fate of his soul.