I just wanted to say, I wish you the best and hope everything works out for you.

Everything has pretty much been covered for you in this thread.

I just want to add, don't be alone with your brother. You're not being crazy, but you need to be assertive - something that you probably haven't done because it's not your personality and you're young.

Stand up for yourself. My younger sister never took shit from me. I tried to be a protective older brother, but she could take care of herself and made sure I knew that. Our father wasn't in the picture, and the few times I tried to stand up for her, she made sure I felt like the younger sibling.

Get your mom in the same room with your brother and preferably some other males (the police?) and make sure he knows he can't do this to you anymore. If he escalates, which he likely will, send his ass to jail - file a police report before hand. Seriously, I know he's your brother, but if he breaks the law (threats, stalking, harassment), he deserves to be in jail.

The police report is important because they have a record of it on hand in case something escalates in the future ("I told you my brother was stalking/threatening/harassing me already, and he's doing it again."). Also, you need to get your mom on the same page. She's obviously your support and she needs to handle this. Tell her you're considering going to the police. Let her know how serious it is.

Know that your brother will likely go to jail after this if he doesn't stop. He deserves this.

He's an adult and you are not even 18 yet. It's incredibly fucked up what he's doing. He should be focusing on his own life instead of creepily obsessing over you. I'm sorry you're dealing with this.