The default parental order is 50/50 for each parent. You both have parental rights to your child and having both parents is the most beneficial. I would start working on a parenting plan with a lawyer.

The way your child feels about his grandparent is irrelevant, however. Nor is where your stbx will be living. That's his choice and he will make his own life decisions in the future, just like you'll make yours. Concentrate on what's important. Finding a way to work out a shared parenting arrangement with your child who needs both of his parents in his life.