There's a lot of smaller issues to break down there. Start by breaking everything you just said into individual pieces. You have,
Loss of energy/motivation, poor attitude
Loss of friends
A personal betrayal
Lack of privacy
Bullying from family
I'll start by saying, the first one is probably depression brought on by the rest. The way to address that is by either changing or coming to terms with whatever is causing it. In the meantime, if you're feeling particularly down stop and think about why you feel that way. Try and find a cause and make note of it so you can address it later.
The loss of friends, how did it happen? Did they change? Did you change? Was it outside influences? You'll have to ask yourself some hard questions to figure out why it happened. And ultimately, ask yourself if it's a bad thing. People change. Maybe you just need new friends. It's hard to give any definitive advice here without knowing all the (probably personal) details.
The personal betrayal, is it related to the above? Something else? What was the issue? Was it a disagreement, or something more? Again, without a lot of details that you don't need to share it's hard to give advice here. But you know you, explore it and figure out what happened and how you feel about it, and use that to decide if that friendship is worth fixing or if you should just move on. You are in control of your life, not them. Don't let their own choices change how you see that.
The lack of privacy is...annoying? It's one of those things that at any one moment doesn't seem like such a big deal (which I'm sure the parent will latch on to in defense of it) but over time it wears you down. Why was the door removed? Can you reach a compromise? Try explaining how it's making you feel and see if you can pin up a sheet or something. There would be no door to stop someone checking on you, but you at least wouldn't feel like you're watched 24/7.