My research supervisor left the university and no one told me
Am I right to be upset that no one informed me that my supervisor was leaving/has left?

While it sounds like your subject (counselling psychology) is much closer than mine (mathematics) to understanding human emotions, I would suggest that it may not be productive to think of emotions in terms of &quot;right&quot; and &quot;wrong&quot;.  I don't know what your personal relationship with your advisor was, or what the norms/expectations are in your field/department with respect to supervisor relationships.  While in most instances, I would expect a supervisor to let their students know personally if they are leaving the institution, it sounds like this may have been a sudden leave and supervisory expectations for masters theses can be quite different than for PhD theses.  (In math in the US, the former is quite rare.)  To continue...

she had informed the head of the department with my name and thesis topic and asked them to check in with me. I was never informed about this change. My supervisor didn’t send me an email to inform me when this happened in June and I still haven’t been contacted by anyone from the department

With the pandemic and other disasters, I would guess that someone accidentally dropped the ball, so you could be upset, or be understanding, or some combination of both, but I don't think that any particular &quot;choice&quot; of these emotions is &quot;right.&quot;
Anyway, after you learned this, did you contact the head of the department?  If not, try this and/or the graduate student director if your department has one.  Presumably your former supervisor's goal was that the head of the department would try to find you a new supervisor under which you can continue your current project.  I don't know how it is in your field/department, but in mine if your thesis was essentially done, we would just have someone else formally complete the supervision even if we don't have an expert in the area.