My fianc� wants to use the diamond from his moms ex marriage...?

Her husband cheated on her and ended up leaving her for another woman, is it wrong for me to feel weird about where the diamond comes from and it's intended meaning as an heirloom? (I don't even care if the ring has a diamond) his mom is alive and well, she is getting rid of some jewelry an asked my fianc� if he wanted the ring or she was going to sell it.