Do I file taxes jointly if we are common law or not legally married?

My boyfriend and I would like to be married ASAP but are thinking about just having a ceremony and no marriage license. He has plenty of government debt and we do not want this to affect me as well. This is why we have not gone through with getting married. If we just have a ceremony and express our love to one another in front of God and our families do we have to file taxes jointly? Will this affect my name? I will change my last name legally also, how do I do this without a marriage license? Please help!!