There are grandparent support groups throughout the United States, and sometimes the burden is eased by sharing with others in similar circumstances. In answer to the woman who wrote because she never knew what to answer when people asked why she'd never married, I think my mother's suggestion was a classic. They married the next month and proceeded to have a life together creating six more children. In 1993 I found my birth parents and siblings. One more time she is missing the joys at her doorstep.
Life goes on.
If opportunity knocks twice, let it in, and don't question everything. So be happy for the opportunity you provided. Your child is. I also think that your healthy outlook can work for a lot of us who spend too much time despairing past actions and regretting that over which we have no control. Thank you for a reasoned, heartfelt letter.