How do I handle a boss who invades my personal space and is gaslighting me?

I have a job that I liked for... awhile. My boss was a little passive aggressive, domineering and controlling in the beginning but I kind of just dealt with it. I'm in my 30s, this job is pretty senior and I left another senior role at another F500 job where I ran board meetings...etc.

In the beginning, it started with making me watch him narrate how to check his email or buy something on the internet (so I could learn?). Every little decision, for some reason, involves watching him do step by step mundane tasks. It will literally take us hours (followed by days of discussion) to order cleaning supplies off the internet. These are all things I could probably do in 20 minutes.

I've dealt with this fairly well for the past 6 months because he has his own office across the hall and spending a few hours every other day is just-about-bearable.

However, about a month ago, he just announced that he wanted to sit in my office. He still has his own office but he moved all of his stuff into my office. He now sits here all day, every day. This means that this "watch-me-check-my-email" happens all the time. A lot of times, its not even work related. He likes to stare at construction out of the window and would make everyone get up from what they're doing and stare out of the window.

He moves stuff around my desk and logs into my computer when I'm not there so I'd come back and essentially find myself gaslighted. He has some OCD problem where he feels the compulsion to pick things up and move it 2 inches away. When he is in a bad mood, he rants and raves the whole time to make sure everyone hears. He mutters under his breath in a loud and obvious way. The other day he said to me, "I wish I had your job."

Today, he decided to watch an instructional video on speaker.

I sit in an enclosed space and there is nowhere else to go. If I leave, he always says something.

This is starting to give me a lot of anxiety. My job isn't stressful but sitting in this office is. I'm naturally an introvert and I haven't gotten anything done since hes started since now my whole day is filled with watching him complete some menial task. I feel like I'm regressing into a small child and I'm worried that when I leave this job, I won't be able to command a room or run a meeting as a fully-functional-senior-leader.

I thought about telling him but I'm 99% sure his ego won't understand how his little "actions" bother everyone around him. He'll either blame me or it'll go on my performance record.

tldr: boss sits in my office and won't leave me alone. Not sure what to do.