Divorce

I've been married for 3 1/2 years and have a child that is 4. A years and a half ago I told him I wanted a divorce. I've been waiting for him to get out of jail, where he has been for the past 3 years for drug charges. He got out about 4 months ago and about three days ago I was served with divorce papers at my work. A guy just walked up to me and ask to talk to me on the side. He gave me the papers and kinda explained them to me. He didn't got though HR or talk to anyone at my work about talking to me. I work in a public place but I was working. I didn't think they could do that without telling someone first. The only thing about the divorce is that he got temporary custody of our son. Now I am not a bad mother. The only thing that I have against me is that I have epilepsy. I work and do everything that other people do. It's a mild case and I take med. for it. I just don't know how they could take my son, who I've raised, away from and give to him. Please I need advice on what to do.