Is it bad parenting to cut my mother (son's grandmother) out of my child's life?

I recently discovered through a "just for fun" ancestry DNA test that I have a different biological father than I've always been told. It's been quite a shock and I'm still processing that information. It turns out that my mom had an affair with her boss and that guy is actually my father.When I first realized something was up with my DNA test (I matched up as sharing a lot of DNA with a man I had never heard of), she made a LOT of excuses about how incorrect those tests are, how it seems like the ancestry bank got their wires crossed, etc and was basically just going to let me search on my own in the hope that I never connected the dots.I did connect the dots and the news is out there now. I've made her tell my biological father. It was also a shock to him (I guess she told him the dates didnt match up for me to be his child, although I imagine he must have also suspected). The man I thought was my father actually left when I was 6, has been pretty absent from my life, and we have been completely estranged for the past decade. Noone even knows where he is to tell him.My mom has a history of making horrible choices and being very deceptive. I've suffered from many of these choices. My childhood wasn't good. We were already not close because of this and I live across the country from her. This is the last straw for me. I don't want a relationship with her at this point. I just don't know if it's fair to my son (10 months old) to not get to know his grandmother (who loves him and dotes on him as much as she can from 3000 miles away). I'm obviously blinded by rage. What's the best parenting choice for my son? via /r/Parenting https://ift.tt/2XxZVdK