Jennie, I understand how you are looking back at your family situation over the years with clear eyes and a different perspective, now that you are sober. I went through something similar and I realized that my family of origin was toxic to me. I had tried to help, cried at my failure to do so and made a decision to step away. This has been a good decision for me. I need peace in my life and I cannot afford to slip back into depression.
My suggestion would be to accept that you might never understand what is happening with your grandfather. It's a 'wait and see' situation, but don't let it pull you back into depression.
I am incredibly blessed that my husband's family is amazing and I love them all and they love me.