You probably have a leak in the pipe up from the pump or from the well to the pressure tank/switch. That assumes the points in switch aren't burnt shut or the switch isn't adjusted wrong.
I don't know how you are keeping antifreeze in the line to the switch but if there is a check valve used to do that, that will prevent the pressure getting to/from the switch. That may be why the pump runs constantly.
A broken bladder can not cause a pump to run constantly.