First of all, amein to your bracha.
Now, before I judge the rebbe, menahel or teacher, I’d like to ask you to take a step back. Where were YOU? Yeah, YOU. You knew you were a good kid with one weakness, why didn’t you ask for help? If you didn’t feel comfortable discussing it with your rebbe, why didn’t you have a talk with your parents? Or daas Torah? Or the rav of your shul? Or a big brother/in law? Or an uncle?
You seem to be a smart kid who knows what’s right and wrong. It doesn’t look like you’re struggling with your Emuna, B”H. All you need, is a little guidance. Perhaps you’re right, maybe they WERE to quick to decide to throw you out – there’s no way I should know since I’m not involved in this. But I think that instead of focusing on THEIR wrongdoing and how bad THEY are, why don’t you spend your energy on thinking how you can better yourself? You don’t seem to be too deeply involved with the “bad crowd” on the streets – baruch Hashem. Before things spiral out of control, SEEK HELP! Don’t just sit back and blame your rebbes. Try being saved! You’ve entered a VERY dangerous zone which is like quicksand. Before you know it, things may get MUCH more complicated chalila. DON’T DO IT! For your sake and for klal yisroel. You said you’re good in gemara. You might end up being a great talmid chacham! Don’t allow this to go to waste.
Look for the right person. Try getting a mentor. Tell them you’re willing to change. I can almost guarantee you that if you are sincere and truly show that your willing and ready to work hard, they’ll accept you with open arms. From experience I tell you – it pays!
(BTW, I’m 18 and I too, struggled this past year. I think being 17 is not easy, but now I can say that all my difficulty truly helped me grow and helped me be what I’m now.)
Hatzlacha rabba.