"fade away" does not come with a direct object. You could say e.g. "... to make your confusion fade away" or "to gradually eliminate your confusion". I prefer my first option. Correction: "I wouldn't be writing this had it not been FOR that letter." No "hence" because conditional clauses ("had it not...") automatically come with consequence clauses. There is no need to use "hence" too.

The first sentence is grammatically correct but the meaning is unclear. Perhaps further context would help us to understand but perhaps also the idea needs to be expressed in different words.