I didn't know the man personally, but I can tell you all this. Beware of books that come out after someone's death claiming to "the truth" about what kind of person they are. Any accusations about someone's character should be made when the person is alive and can defend those accusations.
I did not know Roddenberry but I did meet him on several occasions and talked with him at length. Now while we know Gene cheated (the painful expression of Majel's face during Rod's psudo-documentary was evidence enough), I never saw any behavior to indicate he was as sex crazy as everyone portrays him to be.
If anything I would say he might have been a bit autistic, but that is purely my opinion.