Legally Can I Take Back a Gift I’ve Already Given Someone?

My Crazy Scenario: I moved into an apartment with a friend about 8 months ago. For Christmas he gave me a diamond ring he had intended to give his ex-girlfriend and I gave him a Nintendo Wii. Since that time, he started using drugs and has turned into a monster deadbeat roommate and we are no longer friends. Just a week ago, he was forced to go to a long term rehab by his parole officer. This has left me responsible for both halves of the rent for the next two months until our lease is up. He has no extra money and no intentions of paying his half if he is not here. I still have the receipt and the box for the Nintendo Wii and want to sell it in order to make up for his half of the rent. I can get more money for the Wii than the diamond ring and therefore am willing to give him back the ring and sell the Wii. My question is: Is it legal to do so?