When you cut into brie, the ripping process ceases. So you should eat it within the next several days, or refrigerate it. Though to preserve the rind, you should wrap it in wax or parchment paper, and avoid plastic wrap. Putting it in the freezer is not recommended unless you are making something in which texture doesn’t matter. And it will last up to six months in a freezer safe container.
Throw it away if it sells like ammonia. you can keep brie for a couple of weeks if unopened, but after wards its a week or less. The rind will turn grey and flaky, and pink and green mold spots can form. These are all signs of spoilage and to throw it out immediately.