Please don’t buy a gun.
I can understand owning a little pistol if you’re in a high crime area, and of are sound mind. Even then though if you shoot to kill it can turn into a nasty court case, arrest, and a media debacle.
The FBI doesn’t stalk or harass people. They will only investigate you if you have ties to extremist groups, terrorism, or organized crime.
If anything they probably lecture law enforcement to keep an eye out for the mentally ill in regards to protect us.
Take care and stay safe. It sounds like you’re under a lot of stress. If I’m correct, I think you’re a veteran. I’m also a veteran and I believe in looking out for all veterans.
If your neighbor is harassing you report it to the police and start a paper trail. Do you know how dumb a lawyer can make an instigator look in court?
Be well. 