Hey there First off, have you talked with your mother about your dislike for her choices of boyfriends? Often people are so blinded by the people that they care about that they don't see their faults. If your mother is in love with this person, perhaps she needs you to help give her a wake up call. Especially if he is being a tyrant to the point of selling your family pets. It shouldn't be up to him.
Has his presence ever made you feel so helpless that you considered harming yourself? If it has you definitely need to find a way out immediately. If you told your mom this, she would see how serious the matter is. I'm sure that he is driving you into depression. I would definitely reccoment counseling; if counseling doesn't work you should medicate yourself.
Have you tried talking with the boyfriend about it? Explain to him that you are uncomfortable with his strict rules because he is not your real father. Be respectful since he is your elder; but he may not realize how much he is hurting you. If he reciprocates in a violent way - you need to get out immediately. That showcases that his temper is potentially dangerous. Also, tell your mother if this occurs.
You mentioned that you can't move in with your father because then you couldn't receive your GED. You are forgetting that it is not to late to re-enroll in school. You really have to choose your battles. If you would rather put up with a tyrant of a (potential) step-dad then go back to school it obviously isn't as serious as you are making it sound. Call your father and let him know what's going on. At least talk with him about this.
You mentioned that you dropped out which obviously means you are over the age of fifteen. In this case, you only have a little while left to go as it is. If you want to move out as soon as you can you need to first make yourself financially stable.
Some ways to prepare yourself:
Get a job Go job hunting and find a decent paying job. The harder you work; the sooner you get to move out. You can also start working your way up now so eventually you can become manager. Managers get twice the pay of other employees.
Get a car Do you have a car already? If not, you should save up money to get one so that you can really be independant. After all, when you are on your own you will need a way to get places. A car is a good investment.
Education I know that you alreayd dropped out, but in the end an education is important for your future. You don't want to end up dependant on boyfriends like your mother is do you? Someone who can make themself into something out of nothing is brilliant.
If you ever need any more advice, feel free to respon on here or send me a PM.
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Antidisestablishmentarianism.