Congrats on the almost offers! As someone who recently left a very toxic environment, your quality of life is about to improve! Leaving will be an unpleasant blip on the journey to a much better you!
Remember that you cannot control how boss acts. You can only control how you act.
This is a situation where you just need to plan for you. That is to say, download your contacts, empty your office drawers (but not desktop) of personal stuff so you have less things to take home, make sure you don’t have any personal files on your computer. Submit your expenses first (most states require they be paid by law). Be prepared that the day you give notice may be your last day, if your boss is that toxic.
Have a canned answer for why you’re moving on and practice rehearsing it.
Boss: Why are you leaving?
You: After [X] years, [script].
I will post in the comments a great article that will give you some courage on how to phrase. It’s positioned as a what you should say when you are interviewing, but same idea applies. You’re not there to tell boss the truth–you’re there to say something that sounds neutralish, is plausible, and shuts down conversation.
And also read some advice re exit interviews from Ask a Manager. If this boss is this awful, your company knows, and they don’t care, and it’s reason enough to go.
If boss is going to be vindictive or trash your reputation, that’s going to happen no matter what, and will reflect more on him than you. You do you. Just have your escape plan and your canned response ready. You got this!!!