I think your hormones are causing you to be too sensitive about the situation. When you can think rationally about it, you will realize it is just a ring and rings, no matter what their "sentimental" value is, can be replaced.
My husband bought me a beautiful diamond cross necklace for Christmas one year and I lost it shortly after he gave it to me. I believe it went down the drain in the shower as I found the neck chain, sans the pendent, when I was drying off. We were sad because it was expensive (to us anyway) and very pretty, but my husband didn't think I didn't love him anymore because I was careless enough to lose it.
Your husband may have bought the replacement ring because he wanted to reassure you that he didn't misplace it on purpose so others wouldn't know he's married, or maybe he just bought another ring to keep you from nagging him about his old one. Regardless of the reason, I think it was nice that he went to the trouble and I think you need to realize not a lot of husbands would do that.
Remember to appreciate what you have and don't put so much value on things you've lost. You'll waste too much time and effort worrying about things that are gone and then you'll miss out on enjoying the things, and people, you still have.
Congratulations on your baby on the way!