As an NES but not a teacher, I believe your problem is with unnecessarily long sentences/paragraphs.
Try this reformat - just for clarity:
There were projects that I specifically did not want to be involved in.
Even though I could drop out of them if I wanted to,
I participated in them simply because I didn't have the courage to say "No!".
I was even willing to pay a high price (in health terms) just waiting for someone else to say "No!" for me.
As soon as I realized/realised this, I was able to find the courage to listen to myself and follow my own desires.
Does this help make it clearer?
PS: The person that effectively said "No!" could have been a colleague, a project leader or a health professional, who could see what was happening from "outside".