On the apology letter, I find this helpful internally. Write it up like you plan on giving it to her, but do not. It's a healthy exercise to identify what you think you have done wrong in the past in your R. Work on those things without her knowledge. Better yourself.
Me 42, Wife 39; Married 16; Together 17; Kids: D13, S10 Wife asks for Divorce: 03/19/13 Reconcile: 07/07/13 Round 2 Starts: 02/19/17 Apartment Life: 04/21/17 PA Confirmed: 05/23/17