What will my status be if I marry my girlfriend?

If you marry her your immigration status will remain the same, but she could petition for you once after she becomes a United States citizen.

Just getting married by itself does not change your status. A green card spouse may file an I-130 (first stage of permanent residency ("PR") ) for their spouse without you leaving the U.S.; HOWEVER, just by filing an I-130 does not give you the right to remain in the U.S to await a current Priority Date and ability to file the second stage of the permanent residency. You will need to continue to maintain some nonimmigrant status until it is time to file the second stage of PR. Another concern is that the B-2 is a type of nonimmigrant which requires you to show nonimmigrant intent - filing an I-130 shows immigrant intent so it would be best to also change to another nonimmigrant classification which permits dual intent. Issues are complicated and should be discussed in more depth with an immigration attorney to determine the best and safest strategy after knowing your qualifications, goals, etc. You may arrange a consultation by contacting me.

You have no legal status by virtue of marrying your girlfriend. Once married she has to file an petition for you, and once she is a U.S. Citizen you have to apply for a Green Card. If your girlfriend becomes a U.S. Citizen you can remain in the U.S. after your B2 status expires and apply for your Green Card in the U.S.. If she does not become a U.S. Citizen, then you will have to depart the U.S.