People here are trying to be kind to you and convince you to do the right thing for your bird. They keep saying that your heart is in the right place, and they know that you love Corn. But the way you're treating him makes me wonder--it's very selfish to do what you've done to this little birdie.
If you can't give him a good place to live and take proper care of him, it's selfish and irresponsible to keep him, especially when so many people here have offered to help with finding him a good place to live, a place where he can be happy. You're not considering his feelings and his needs, which is what people do when they really love someone else.
A dark box is a bad place to keep a chicken. You've read it here, and you know it to be true... but because you don't want to give him away, you think it's love to keep him. It's not love. It's very hurtful to your bird, and that's not love... that's not having your heart in the right place. If your heart was in the right place, you'd be more concerned about what he needs than what you want.
Don't blame your parents for not helping you enough. You're the only one he has. He can't talk to you in words, he can only show you how he feels in his behavior and his health. What has he been telling you with those things?
If you want to show that I'm wrong about you not loving your bird, it would make me happy. To do that, you'd either have to find him a good home with someone who can give him all the things he needs--NOT a neighbor or friend who will agree to keep the bird in a cardboard box for you--or you'd have to get him the proper things he needs NOW.
If you can't convince your parents to help you take proper care of him, and if you REALLY love him, you still need to make sure he has what he needs and find a better home for him NOW. Not later. Don't make him suffer like that any more if you love him.