Personally, I would be looking for an exit, either mine or his.
Be wary of this. HR exists to protect the company and void litigation, not necessarily to protect the employee or the employee's work environment.
@OP consider asking for advice on https://workplace.stackexchange.com
"The enemy of my enemy is my friend"
I don't think this is good advice. Sorry.
If boss person is monitoring communications, it's 99% likely this is happening within the policy guidelines of your company.
As mentioned above, HR is not your friend. I would think of HR as a place where you can document your future lawsuit and buy you a little time to find another job.
I had an issue with another programmer, (homophobic slur and he was getting cozy with the client/boss) so feared for my job. I filed a complaint and got it documented. It allows you maybe 6 months before they fire you or buys you sometime to get in a better space.
Although it's fun to think about suing your previous employer, it very rarely works out. That energy can be spent finding a better job.
There is a time to fight... but from what little I know, this doesn't sound like one of them.
p.s. I'm no longer at the job and have moved on and even more happier.
Mitigate it in the meantime; these CYA strategies are good advice (except maybe the HR one), but most importantly, RUN AWAY AS SOON AS YOU CAN.
Agreed. If you have options, leave. You can't fix jerks. Then again, every job will have some, but if it's your supervisor, then polish up your resume. The stress is not worth your health.