How do I deal with having a girlfriend with split personalities and skitzo? And is there any treatment for it. Weither fda aproved or not

Skitzo girlfriend. I'll go out on a limb here, and guess that your girlfriend is niether schizophrenic (which does not mean multiple personalities), nor has mult. Personalities, but rather tends to vacillate between extreme moods, and maybe even gets a little psychotic when under severe stress. You should both really go in for a psychiatric eval., to better understand what to expect, and options, moving forward.
Many treatments. There are treatments for schizophrenia and multiple personality disorder. This is a complex issue and should be treated by a skilled psychiatrist. As the significant other, you can help by being as supportive as possible.
P.S. In cases of borderline personality disorder (which, incidentally, this may or may not be) simply being "supportive as possible" can actually serve to reinforce negative behaviors, and is thus extremely counterproductive. Reference "dialectic behavioral therapy" - notably; the only (statistically proven) effective treatment for this fairly common disorder.