Robin, what you're describing (multiple personalities) is technically called dissociative disorder. Of course no one can diagnose via the internet, but here's some info.
A snip from NAMI | Dissociative Identity Disorder (formerly Multiple Personality Disorder)
"Dissociative Identity Disorder (DID), previously referred to as multiple personality disorder (MPD), is a dissociative disorder involving a disturbance of identity in which two or more separate and distinct personality states (or identities) control the individual's behavior at different times. When under the control of one identity, the person is usually unable to remember some of the events that occurred while other personalities were in control. The different identities, referred to as alters, may exhibit differences in speech, mannerisms, attitudes, thoughts, and gender orientation. The alters may even differ in "physical" properties such as allergies, right-or-left handedness, or the need for eyeglass prescriptions. These differences between alters are often quite striking."
There's a little more on the link I put above, and you can also Google it to get even more info. The major "cause" for this disorder is childhood trauma, where the person assumes an alter who is "stronger" in some way to handle the trauma.
You're lucky you discovered this about him before your relationship went any further. I'm glad you're safe, and I offer more *hugs*.