Just hold your ground and keep reading your book, eating alone etc. If someone enters personal territory, shut it down by being honest "I don't want to talk about that" and move on. Resist peer pressure and be who you are, it's the same as it was in school.
Also, talk to your coworkers (I know it's hard) about whether they think it's appropriate. You have an impression they're on board with this level of "intimacy" but it's possible they are just going along to get along.
If persisting doesn't work then it's probably time to find another job. Plenty of workplaces out there that just want you to do your job and no more.
HR is definitely not on your side either, unless you can point to specific violations of policy. They exist specifically to cover their own ass, not to actually make your life better.
Yeah, but you see they were in danger from the Vietnam draft, doesn't take empathy to act in self interest.