First, I'm sorry you and your child have had to go through this disturbing experience at school. Whether or not he exhibits behavioral patterns that increase his visibility as a target, it is not his fault when someone else chooses to use threatening language or actions toward him. I hope he is understanding the message that you are doing what you need to do to keep him safe, including possibly homeschooling.
With regard to your alone time: sometimes you can prepare the homeschooling scenario for your child in terms of "going to work". If he is sufficiently independent to do online school with minimal hands-on support from you, you may be able to set up a room with a door to be his "office"--or a room with a door to be -your- office. During "work hours", you each go to your office and do your work. Maybe you come out and chat for a few minutes during morning coffee/milk break, lunch, and afternoon snack time, but while at work, you each do your work.
You can also just say that the morning is school (most kids on this forum can probably finish a day's worth of online school in 3 or 4 hours, or less), and then the afternoon is his free reading, creative, or workshop time. Provide him with the necessary materials/books/workspace, and then say that this is your time to recharge yourself in your way (aka, alone), and his time to recharge himself in his own (safe, obviously) ways, or work on personal interest projects, for a couple of hours.
You might give a few minutes to thinking about exactly how much solitude you require per day for your own mental health, and then try to either set up his school day with those office hours in mind, or perhaps have a conversation with your husband about setting aside some alone time for yourself when he's home from work.
Depending on his age, you can also look for drop-off enrichment classes or clubs in your homeschool or larger community (they do exist in many places), to give yourself an hour or two during the week where he's engaged in something outside of the home. Try also museums, libraries, afterschool programs, even some stores (Lego, Apple, Joann Fabrics, Michael's, Hobby Lobby, Lowe's, Home Depot).
