I honestly would probably give it back. I wouldn't give him the satisfaction and he would just use the issue to bother you. When I was parting ways with my ex and he was moving out he grabbed a pair of diamond stud earrings that he bought me one year for my birthday and said he was selling them. Although it hurt I didn't let it show
I simply told him he bought them he can do whatever he wants with them. I think it stunned him because he ended up leaving them.