I've been in a similar situation.

I had to grieve the relationship, face facts, and focus on having a good life with my son. My son turned out just fine. My son does not resent me for taking good care of him.

You could probably get sole custody. You can be in counseling now and also work out a safe plan for when and if he sees your son.

When your son is older he can then try to have a relationship with his father or not. His father may never be capable of one.

The safety of you and your son comes first.

I completely understand the wish that the guy would just have something major and understood like a brain tumor.