Grieving can take a long time. Let yourself have space and time for it and don't try to push it away. My therapist told me it typically takes about 3 years to grieve the loss of the marriage and spouse, even when you want to split up.

If your son's father is not fit to share custody with you, then perhaps he can have supervised visits and see your son occasionally with a responsible "chaperone" present. You can get this written into your parenting plan and approved by the court. A friend of mine has a mentally ill ex-husband who is only allowed to see their kids with supervision.