You are moving physically in a couple of weeks, might be time to also move on, emotionally.
Mike said it all, it was a gift to him, let it go. To me, if it had so much sentimental attachment, I would have never given it to anyone, it's too late now.
He doesn't need any excuse to not return the ring, it's his.
I must agree with Anvil, I believe that you want to be in contact with him, and, the ring is a good excuse.