So Battlefield 3 is free to Origin members and once it's downloaded it it's yours to keep, according to the On the House page of the Origin website.
You can get it for free until the third of June.
Get it here: https://www.origin.com/en-gb/store/buy/battlefield-3/pc-download/base-game/standard-edition
You can get it for free until the third of June.
Get it here: https://www.origin.com/en-gb/store/buy/battlefield-3/pc-download/base-game/standard-edition