I am so sorry for such a terrific loss! I always wondered if I would survive the loss of a child. I understand you wondering about life from here forward. We lose loved ones and we think the whole world should end... but it doesn't. Life goes on. You have a son left that needs you very much and a grandchild. You said this child will never know their dad like you did. That's true. But you have to keep putting one foot in front of the other and keep your son alive in everyone's heart, especially that child!
Right now, though, you need to get through your own grief. It is still very fresh. There are support groups in almost every area that deal with grief of a loved one. Call your County Mental Health Dept and see if they have one going or are planning to start another. I think Hospice also has them.
As selfish at it may seem, you need to take care of YOU first so that you can help your loved ones that are also suffering the same loss.
You came to the right place. Keep posting, keep writing, keep crying, keep talking about it. You'd be amazed at how much it helps.
We'll be here to support you through this.
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Psalm 119:105 Thy word is a lamp unto my feet, and a light unto my path.