Legal Question in Immigration Law in California

If you want to remain in the United States legally, you should find a way to change to another non-immigrant visa status. Otherwise, assuming you get married, you cannot file for adjustment of status (& a work permit) until your girlfriend becomes a U.S. citizen. If you overstay your visa now, you risk being "out of status" (i,e, "illegal") for over one year, which is never recommended.

There are several types of non-immigrant visas, however, you might not qualify or be interested in them. I recommend you speak with an experienced Immigration Attorney in person regarding your options.