Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.

And don't be so quick to think that the way you see it is how it is. Your sister is probably ensuring that the connection with your family is protected so that you all still have access to your son.
Just because you feel bad right now doesn't mean anyone else is doing something wrong. It make take you some time to get over this devastation, but make sure you don't do or say anything to burn your bridges. You need to let go of your feelings and be tactically wiser now. You have more to lose.