Travel and Leaving in Argentina

I am Russian-American who two years ago found love in Argentina, and planning to move and live there now. I know that I don't need travel visa for 90 days, but after that how can I keep legal status? Can I leave and return in a week or so? Or there is the specific time that I need to stay in the United States before entering the country again? Please direct me to the good site or forum where I can find details for immigration. Thank you!