It is certainly possible that your brain was damaged as a result of a high fever but there is no way to know for certain. Thankfully, you successfully overcame that health trauma, against all the odds.
Your question is difficult to answer because there are many variables. In addition to the possible brain damage you may have sustained, you endured multiple abusive situations. Many individuals with depression have a history of abuse. There seems to be a definite correlation between the two but rarely can clear cause-and-effect relationships be delineated. Even if you were able to ascertain a definitive answer to your question, it would do little if anything to improve your depression. The “why” is often much less important than finding a cure.
If you are not in treatment, then you should be. Very effective treatments for post-traumatic stress disorder (PTSD) exist. You may also benefit from less traditional though often very effective treatments such as hypnosis or Eye Movement Desensitization and Reprocessing (EMDR). Hypnosis has been shown to help relieve depression, cure phobias and to heal traumas. It has also been shown to effectively reduce anxiety, the urge to smoke cigarettes and to assist individuals in achieving their weight loss goals. EMDR is a form of highly structured psychotherapy used to treat symptoms related to past traumas. Both types of therapies are certainly worth exploring.
Click the find help tab at the top of this page to help you locate a therapist in your community. If you choose to pursue hypnosis or EMDR, choose someone who has solid credentials and a proven track record. I’m sorry that I was unable to give you a definitive answer to your question. Please take care. I wish you well.