Aw, the million dollar question...to be honest, I haven't completely decided on an answer yet.  When I began the story, I intended for Harry to remain a slave, because I said he was example of how a person's life could be changed by an accident or a disease, and how they have to adjust to it, but can still live a full and rewarding life.  That's how I'm seeing Harry's case, and I thought (and still do think) that it could be life-affirming to write the story that way.

But lately I've also been thinking that maybe I would find a way to free Harry either in this story or in the sequel, and give it that perfect happy ending. 

As for Harry being depressed, yes, he is right now.  This is a really hard time for him...it's only been a few weeks since Sirius died and he's grieving and blaming himself. He's fallen victim to the slavery spell, which has had a profound effect on his life and the way he feels about himself, and he's facing the fact that he's the only person who can defeat Voldemort.  So yeah, poor Harry really does have a lot on his shoulders.  It's hard for me to write him like this sometimes, but I am trying to imagine how he would feel at this point in time, trying to deal with these heavy burdens that have fallen on him. 

Things will get better for Harry.  It helps me to know all the things I have planned for him in the future, but I want "Slave Child" to be a long story so I'm trying to take my time and show all the details of his daily life with Severus and it's important to show how Severus is slowly changing and learning to care for Harry, or their future relationship won't be as believable, imo.  So even though Harry is very unhappy and depressed now, and will be for a while still, I do hope that if people hang in there til the end of this little saga, they'll be satisfied with the ending, I hope!