TotallyADD-- I feel your pain. Not sure how old your kids are, but my middle son is now 23 and I am realizing why we have not been close for many years until recently. He is working through his issues of everything I did wrong as a mother and he used to blame me for everything (I was a single mom).
As young people change & grow up, they go through a lot of different stages. When they are really little, they think their parents walk on water, when they are teenagers they think their parents are bad etc, when they become young adults-- they blame their parents for everything until they realize their parents did the best they could. But some people never really get that epithamy that their parents did the best they could. My childhood was extremely dysfunctional and I did blame my parents for many many years, until one day I realized they did the best they knew how because they were emotionally sick. Now I really am amazed by my parents' accomplishments, (but not their parenting skills obviously).
Your letter was perfect. It was short and loving and non blaming. I hope your son will have an epithamy one day and see that you did your best.