SH... read your post from last night. You said, "... in the few days since I came to this, I've been in situations with others where I began to say or do something and it dawned on me I was about to do it."
You are, in fact, changing that in you. Congratulations!
What would you be doing if you gave the apology? Hint... think... "more of the same"...
Here's a suggestion. Get a piece of paper. On it... write all the things you want to apologize for. Point form is fine. Update it as necessary. Keep it handy and keep it private... Then... IF you ever right "that" letter to your W... you are half way there...