I'm sure you will decide what to do for the best, sinking, but if you are experiencing dark and sui thoughts then IMO you need someone to support you. NOT like current T. But someone in your life who you can share these things with, and who will be supportive. They are heavy thoughts and feelings to be carrying alone.
Maybe contacting old T could be a good idea? Or a new T?
Regarding your parents: do you have to explain to them? Could you just say you decided to change T? Or even not tell them? Or make up a reason - that T is cutting down her hours or something?