Advice on what to do about academic situation that ended badly?
I also feel terrible every day about what I said to the Head of Department. They were the best teacher I’d ever had and they are also one of the foremost scholars in my current field. 


I think what you said to the Head of Department should have been expected and I think you should have been better supported. 


  ‪My question is whether I should try to reach out to this academic to explain what happened to me and why I acted how I did and to apologise? 


Given that you feel terrible, I think this might be a good idea.


  If so, how should I do it? Via email, or in person? 


Personally, I'd write a handwritten letter, and open the possibility for a future in-person meeting.  Ultimately, you should make contact however you feel the most comfortable.


  Or maybe it’s too late? 


It's never too late.



Before proceeding, you could talk to a professional.