Which is the best way to apply for a permit in Norway as a non Eu citizen? Family immigration or work application?

Dear all, I am a Brazilian citizen and I have recently moved to Norway with my Romanian girlfriend. She has a 100% contract in Tromsø and I am still with a tourist visa. We have been in a relationship for more than 2 years, but we cannot prove it with documents or rent contracts because we have been working on a ship where we met. Usually contracts are of minimum 6 months, so every time we finished a contract we did holidays together and then embarked again. On the ship the company did not give us a separate cabin because only married couples have that privilege. We only have photos and the fact that this year my salary went on my girlfriends account due to some credit card issues. On the other hand, I shall sign a 60% contract with a restaurant. I have graduated Marketing in Brazil, so it has nothing to do with my job as a cook. My tourist visa expires in one month, and I am a little bit confused about which way to apply, as a cohabitant of my Romanian girlfriend or pay the fee for the work permit? But I have to apply as a seasonal worker which only allows me to stay for a few months. Please reply as soon as possible. Thank you. Best regards, Rafael& Aurelia