Your question is actually more complicated than it seems. If you get married, what rights you will have in the property will depend on if the property is community property, quasi-community property, or separate property.
Instead of wondering about your legal rights, it's best to work this out before you get married. Have an honest discussion with your GF about the house and your contributions to it.
She may see it differently than you do; that you are paying what would be rent. Whereas, you see your contribution as paying down the mortgage.
Answered on Feb 27th, 2016 at 8:15 PM