Well, it's not that you are still suffering after 40 years even though it feels like it. It's more that as we get older we can realize more that how we were treated or felt growing up was stressful and we deserved better. However, the other thing one has to consider is that a lot more is known "now" then years ago and often parents did not realize how wrong they were in how they raised their children and that whatever they lacked in their knowledge could end up challenging that child for the rest of that child's life.
I think the hard part that triggered you is that you don't want to have to explain to your bf why you don't want to include your family in your life, and that means even sending them a card.
Holidays are the busiest time of year for therapists because of the reminders and challenges that can bring back emotional challenges.