I am in the middle of a divorce (I'm the one filing, my stbx-H had an affair but wants to reconcile), but no, I would not return the ring. He hasn't asked for it, but like bridgestone wrote: it was a gift and there's no reason to return it.
In your heart, do you really want the ring itself back or do you want to use it as way of seeing if she'll get emotional as a test of if she might have the tiniest sliver of feeling towards the "symbol of love/commitment."
If my stbx asked me, I would tell him no. But if he pushed on it, I would give it back, and maybe have about 10 mins of being sad, but I wouldn't get upset over a piece of jewelry. When you get down to it, you're right..it's just a symbol.
