Please call a hotline for help. Talk to someone. They might be able to help you see options you haven't thought of.
Nobody is going to take your son away and "throw you into an institution." You do need treatment for your depresssion. Many, many people suffer with depression even when they don't have alcoholic husbands and a baby to care for. It isn't a disgrace, and it isn't hopeless. And it IS treatable.
When you are depressed, you can't see options that are actually there. It's part of what being depressed is--inability to think clearly or to take actions that will help.
If you can't call a friend or family member, please call the hotline. Someone who is trained to help can talk to you, and a voice can be very comforting at times like this.
Many hugs, sweetie, you are gonna be OK again.